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Benefit Plans 2 (Details) - USD ($)
$ in Millions
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class $ 5,015.4 $ 4,695.9 $ 5,174.1
Year End Allocation      
Total 100.00% 100.00%  
Pension Plan [Member] | AEP Texas Inc. [Member]      
Allocated Assets of Investments 8.70% 8.70%  
Pension and Other Postretirement Plans' Assets      
Asset Class $ 435.1 $ 410.7 455.9
Pension Plan [Member] | Appalachian Power Co [Member]      
Allocated Assets of Investments 12.70% 12.60%  
Pension and Other Postretirement Plans' Assets      
Asset Class $ 637.0 $ 593.3 651.7
Pension Plan [Member] | Indiana Michigan Power Co [Member]      
Allocated Assets of Investments 12.60% 12.40%  
Pension and Other Postretirement Plans' Assets      
Asset Class $ 630.5 $ 583.8 636.7
Pension Plan [Member] | Ohio Power Co [Member]      
Allocated Assets of Investments 10.00% 9.90%  
Pension and Other Postretirement Plans' Assets      
Asset Class $ 499.1 $ 466.1 509.1
Pension Plan [Member] | Public Service Co Of Oklahoma [Member]      
Allocated Assets of Investments 5.50% 5.60%  
Pension and Other Postretirement Plans' Assets      
Asset Class $ 276.2 $ 261.2 287.8
Pension Plan [Member] | Southwestern Electric Power Co [Member]      
Allocated Assets of Investments 5.90% 6.00%  
Pension and Other Postretirement Plans' Assets      
Asset Class $ 296.9 $ 281.0 311.7
Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class $ 1,781.8 $ 1,534.2 1,732.5
Year End Allocation      
Total 100.00% 100.00%  
Other Postretirement Benefit Plans [Member] | AEP Texas Inc. [Member]      
Allocated Assets of Investments 8.30% 8.50%  
Pension and Other Postretirement Plans' Assets      
Asset Class $ 148.1 $ 129.9 147.3
Other Postretirement Benefit Plans [Member] | Appalachian Power Co [Member]      
Allocated Assets of Investments 15.20% 15.50%  
Pension and Other Postretirement Plans' Assets      
Asset Class $ 271.0 $ 238.4 273.4
Other Postretirement Benefit Plans [Member] | Indiana Michigan Power Co [Member]      
Allocated Assets of Investments 12.10% 12.20%  
Pension and Other Postretirement Plans' Assets      
Asset Class $ 216.3 $ 187.3 211.1
Other Postretirement Benefit Plans [Member] | Ohio Power Co [Member]      
Allocated Assets of Investments 11.10% 11.40%  
Pension and Other Postretirement Plans' Assets      
Asset Class $ 197.1 $ 175.4 198.5
Other Postretirement Benefit Plans [Member] | Public Service Co Of Oklahoma [Member]      
Allocated Assets of Investments 5.50% 5.50%  
Pension and Other Postretirement Plans' Assets      
Asset Class $ 98.0 $ 84.3 95.5
Other Postretirement Benefit Plans [Member] | Southwestern Electric Power Co [Member]      
Allocated Assets of Investments 6.60% 6.40%  
Pension and Other Postretirement Plans' Assets      
Asset Class $ 117.2 $ 98.5 $ 110.4
Other [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 1,337.3 1,127.5  
Other [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 449.3 393.4  
Level 1 [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 991.1 661.2  
Level 1 [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 649.1 515.6  
Level 2 [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 2,687.0 2,907.2  
Level 2 [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 683.4 625.2  
Level 3 [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
Level 3 [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
Equity Securities [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class $ 1,544.2 $ 1,049.8  
Year End Allocation      
Total 30.80% 22.40%  
Equity Securities [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class $ 824.5 $ 649.7  
Year End Allocation      
Total 46.30% 42.30%  
Equity Securities [Member] | Other [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class $ 547.3 $ 370.1  
Equity Securities [Member] | Other [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 260.8 226.2  
Equity Securities [Member] | Level 1 [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 996.9 661.4  
Equity Securities [Member] | Level 1 [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 563.7 419.2  
Equity Securities [Member] | Level 2 [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 18.3  
Equity Securities [Member] | Level 2 [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 4.3  
Equity Securities [Member] | Level 3 [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
Equity Securities [Member] | Level 3 [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
Domestic [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class $ 387.8 $ 277.3  
Year End Allocation      
Total 7.80% 5.90%  
Domestic [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class $ 312.2 $ 233.3  
Year End Allocation      
Total 17.50% 15.20%  
Domestic [Member] | Other [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class $ 0.0 $ 0.0  
Domestic [Member] | Other [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
Domestic [Member] | Level 1 [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 387.8 277.3  
Domestic [Member] | Level 1 [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 312.2 233.3  
Domestic [Member] | Level 2 [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
Domestic [Member] | Level 2 [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
Domestic [Member] | Level 3 [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
Domestic [Member] | Level 3 [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
International [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class $ 609.1 $ 384.1  
Year End Allocation      
Total 12.10% 8.20%  
International [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class $ 251.5 $ 185.9  
Year End Allocation      
Total 14.10% 12.10%  
International [Member] | Other [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class $ 0.0 $ 0.0  
International [Member] | Other [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
International [Member] | Level 1 [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 609.1 384.1  
International [Member] | Level 1 [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 251.5 185.9  
International [Member] | Level 2 [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
International [Member] | Level 2 [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
International [Member] | Level 3 [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
International [Member] | Level 3 [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
Options [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class   $ 18.3  
Year End Allocation      
Total   0.40%  
Options [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class   $ 4.3  
Year End Allocation      
Total   0.30%  
Options [Member] | Other [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class   $ 0.0  
Options [Member] | Other [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class   0.0  
Options [Member] | Level 1 [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class   0.0  
Options [Member] | Level 1 [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class   0.0  
Options [Member] | Level 2 [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class   18.3  
Options [Member] | Level 2 [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class   4.3  
Options [Member] | Level 3 [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class   0.0  
Options [Member] | Level 3 [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class   0.0  
Common Collective Trusts [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class $ 547.3 $ 370.1  
Year End Allocation      
Total 10.90% 7.90%  
Common Collective Trusts [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class $ 260.8 $ 226.2  
Year End Allocation      
Total 14.70% 14.70%  
Common Collective Trusts [Member] | Other [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class $ 547.3 $ 370.1  
Common Collective Trusts [Member] | Other [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 260.8 226.2  
Common Collective Trusts [Member] | Level 1 [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
Common Collective Trusts [Member] | Level 1 [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
Common Collective Trusts [Member] | Level 2 [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
Common Collective Trusts [Member] | Level 2 [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
Common Collective Trusts [Member] | Level 3 [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
Common Collective Trusts [Member] | Level 3 [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
Fixed Income [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class $ 2,656.8 $ 2,852.8  
Year End Allocation      
Total 53.00% 60.70%  
Fixed Income [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class $ 707.9 $ 622.7  
Year End Allocation      
Total 39.70% 40.60%  
Fixed Income [Member] | Other [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class $ 0.0 $ 0.0  
Fixed Income [Member] | Other [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 177.6 163.6  
Fixed Income [Member] | Level 1 [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class (5.8) 0.2  
Fixed Income [Member] | Level 1 [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 58.7 42.0  
Fixed Income [Member] | Level 2 [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 2,662.6 2,852.6  
Fixed Income [Member] | Level 2 [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 471.6 417.1  
Fixed Income [Member] | Level 3 [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
Fixed Income [Member] | Level 3 [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
Common Collective Trust - Debt [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class $ 177.6 $ 163.6  
Year End Allocation      
Total 10.00% 10.70%  
Common Collective Trust - Debt [Member] | Other [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class $ 177.6 $ 163.6  
Common Collective Trust - Debt [Member] | Level 1 [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
Common Collective Trust - Debt [Member] | Level 2 [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
Common Collective Trust - Debt [Member] | Level 3 [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
United States Government and Agency Securities [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class $ 1,242.8 $ 1,512.7  
Year End Allocation      
Total 24.80% 32.20%  
United States Government and Agency Securities [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class $ 214.3 $ 181.7  
Year End Allocation      
Total 12.00% 11.80%  
United States Government and Agency Securities [Member] | Other [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class $ 0.0 $ 0.0  
United States Government and Agency Securities [Member] | Other [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
United States Government and Agency Securities [Member] | Level 1 [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class (5.8) 0.2  
United States Government and Agency Securities [Member] | Level 1 [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class (0.1) 0.2  
United States Government and Agency Securities [Member] | Level 2 [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 1,248.6 1,512.5  
United States Government and Agency Securities [Member] | Level 2 [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 214.4 181.5  
United States Government and Agency Securities [Member] | Level 3 [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
United States Government and Agency Securities [Member] | Level 3 [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
Corporate Debt [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class $ 1,143.7 $ 1,082.9  
Year End Allocation      
Total 22.80% 23.00%  
Corporate Debt [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class $ 206.7 $ 188.6  
Year End Allocation      
Total 11.60% 12.30%  
Corporate Debt [Member] | Other [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class $ 0.0 $ 0.0  
Corporate Debt [Member] | Other [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
Corporate Debt [Member] | Level 1 [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
Corporate Debt [Member] | Level 1 [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
Corporate Debt [Member] | Level 2 [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 1,143.7 1,082.9  
Corporate Debt [Member] | Level 2 [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 206.7 188.6  
Corporate Debt [Member] | Level 3 [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
Corporate Debt [Member] | Level 3 [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
Foreign Debt [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class $ 211.6 $ 221.6  
Year End Allocation      
Total 4.20% 4.70%  
Foreign Debt [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class $ 35.5 $ 35.0  
Year End Allocation      
Total 2.00% 2.30%  
Foreign Debt [Member] | Other [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class $ 0.0 $ 0.0  
Foreign Debt [Member] | Other [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
Foreign Debt [Member] | Level 1 [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
Foreign Debt [Member] | Level 1 [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
Foreign Debt [Member] | Level 2 [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 211.6 221.6  
Foreign Debt [Member] | Level 2 [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 35.5 35.0  
Foreign Debt [Member] | Level 3 [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
Foreign Debt [Member] | Level 3 [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
State and Local Government [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class $ 55.1 $ 28.2  
Year End Allocation      
Total 1.10% 0.60%  
State and Local Government [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class $ 73.6 $ 53.6  
Year End Allocation      
Total 4.10% 3.50%  
State and Local Government [Member] | Other [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class $ 0.0 $ 0.0  
State and Local Government [Member] | Other [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
State and Local Government [Member] | Level 1 [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
State and Local Government [Member] | Level 1 [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 58.8 41.8  
State and Local Government [Member] | Level 2 [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 55.1 28.2  
State and Local Government [Member] | Level 2 [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 14.8 11.8  
State and Local Government [Member] | Level 3 [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
State and Local Government [Member] | Level 3 [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
Other - Asset Backed [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class $ 3.6 $ 7.4  
Year End Allocation      
Total 0.10% 0.20%  
Other - Asset Backed [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class $ 0.2 $ 0.2  
Year End Allocation      
Total 0.00% 0.00%  
Other - Asset Backed [Member] | Other [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class $ 0.0 $ 0.0  
Other - Asset Backed [Member] | Other [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
Other - Asset Backed [Member] | Level 1 [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
Other - Asset Backed [Member] | Level 1 [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
Other - Asset Backed [Member] | Level 2 [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 3.6 7.4  
Other - Asset Backed [Member] | Level 2 [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.2 0.2  
Other - Asset Backed [Member] | Level 3 [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
Other - Asset Backed [Member] | Level 3 [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
Infrastructure [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class $ 85.8 $ 72.2  
Year End Allocation      
Total 1.70% 1.50%  
Infrastructure [Member] | Other [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class $ 85.8 $ 72.2  
Infrastructure [Member] | Level 1 [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
Infrastructure [Member] | Level 2 [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
Infrastructure [Member] | Level 3 [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
Real Estate [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class $ 239.4 $ 220.4  
Year End Allocation      
Total 4.80% 4.70%  
Real Estate [Member] | Other [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class $ 239.4 $ 220.4  
Real Estate [Member] | Level 1 [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
Real Estate [Member] | Level 2 [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
Real Estate [Member] | Level 3 [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
Alternative Investments [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class $ 448.3 $ 444.6  
Year End Allocation      
Total 8.90% 9.50%  
Alternative Investments [Member] | Other [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class $ 448.3 $ 444.6  
Alternative Investments [Member] | Level 1 [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
Alternative Investments [Member] | Level 2 [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
Alternative Investments [Member] | Level 3 [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
Trusted Owned Life Insurance [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class $ 211.8 $ 203.8  
Year End Allocation      
Total 11.90% 13.30%  
Trusted Owned Life Insurance [Member] | Other [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class $ 0.0 $ 0.0  
Trusted Owned Life Insurance [Member] | Level 1 [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
Trusted Owned Life Insurance [Member] | Level 2 [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 211.8 203.8  
Trusted Owned Life Insurance [Member] | Level 3 [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
International Equities [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class $ 60.2 $ 49.4  
Year End Allocation      
Total 3.40% 3.20%  
International Equities [Member] | Other [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class $ 0.0 $ 0.0  
International Equities [Member] | Level 1 [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
International Equities [Member] | Level 2 [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 60.2 49.4  
International Equities [Member] | Level 3 [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
United States Bonds [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class $ 151.6 $ 154.4  
Year End Allocation      
Total 8.50% 10.10%  
United States Bonds [Member] | Other [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class $ 0.0 $ 0.0  
United States Bonds [Member] | Level 1 [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
United States Bonds [Member] | Level 2 [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 151.6 154.4  
United States Bonds [Member] | Level 3 [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
Cash and Cash Equivalents [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class $ 61.6 $ 47.8  
Year End Allocation      
Total 1.20% 1.00%  
Cash and Cash Equivalents [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class $ 33.4 $ 59.2  
Year End Allocation      
Total 1.90% 3.90%  
Cash and Cash Equivalents [Member] | Other [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class $ 37.2 $ 11.9  
Cash and Cash Equivalents [Member] | Other [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 6.7 4.8  
Cash and Cash Equivalents [Member] | Level 1 [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 (0.4)  
Cash and Cash Equivalents [Member] | Level 1 [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 26.7 54.4  
Cash and Cash Equivalents [Member] | Level 2 [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 24.4 36.3  
Cash and Cash Equivalents [Member] | Level 2 [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
Cash and Cash Equivalents [Member] | Level 3 [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
Cash and Cash Equivalents [Member] | Level 3 [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
Other - Pending Transactions and Accrued Income [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class $ (20.7) $ 8.3  
Year End Allocation      
Total (0.40%) 0.20%  
Other - Pending Transactions and Accrued Income [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class $ 4.2 $ (1.2)  
Year End Allocation      
Total 0.20% (0.10%)  
Other - Pending Transactions and Accrued Income [Member] | Other [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class $ (20.7) $ 8.3  
Other - Pending Transactions and Accrued Income [Member] | Other [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 4.2 (1.2)  
Other - Pending Transactions and Accrued Income [Member] | Level 1 [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
Other - Pending Transactions and Accrued Income [Member] | Level 1 [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
Other - Pending Transactions and Accrued Income [Member] | Level 2 [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
Other - Pending Transactions and Accrued Income [Member] | Level 2 [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
Other - Pending Transactions and Accrued Income [Member] | Level 3 [Member] | Pension Plan [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class 0.0 0.0  
Other - Pending Transactions and Accrued Income [Member] | Level 3 [Member] | Other Postretirement Benefit Plans [Member]      
Pension and Other Postretirement Plans' Assets      
Asset Class $ 0.0 $ 0.0