Summary of Investments Other Than Investments In Related Parties (Details)1 (USD $) In Millions, unless otherwise specified	Dec. 31, 2012
Fixed Maturities [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Cost or amortized cost	$ 8,222
Fair value	9,093
Balance sheet	9,093
Equity Securities [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Cost or amortized cost	2,369
Fair value	3,373
Balance sheet	3,373
Other than Securities Investment [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Cost or amortized cost	68
Balance sheet	68
States, Municipalities And Political Subdivisions [Member] | Fixed Maturities [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Cost or amortized cost	3,040
Fair value	3,289
Balance sheet	3,289
States, Municipalities And Political Subdivisions [Member] | Fixed Maturities [Member] | Cincinnati Casualty Company [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Cost or amortized cost	123
Fair value	133
Balance sheet	133
States, Municipalities And Political Subdivisions [Member] | Fixed Maturities [Member] | Cincinnati Indemnity Company [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Cost or amortized cost	36
Fair value	39
Balance sheet	39
States, Municipalities And Political Subdivisions [Member] | Fixed Maturities [Member] | Cincinnati Insurance Company [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Cost or amortized cost	2,528
Fair value	2,717
Balance sheet	2,717
States, Municipalities And Political Subdivisions [Member] | Fixed Maturities [Member] | Cincinnati Life Insurance Company [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Cost or amortized cost	200
Fair value	230
Balance sheet	230
States, Municipalities And Political Subdivisions [Member] | Fixed Maturities [Member] | CSU Producers Resources Inc. [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Cost or amortized cost	1
Fair value	1
Balance sheet	1
States, Municipalities And Political Subdivisions [Member] | Fixed Maturities [Member] | Cincinnati Specialty Underwriters Insurance Company [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Cost or amortized cost	152
Fair value	169
Balance sheet	169
Convertibles And Bonds With Warrants Attached [Member] | Fixed Maturities [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Cost or amortized cost	31
Fair value	31
Balance sheet	31
Convertibles And Bonds With Warrants Attached [Member] | Fixed Maturities [Member] | Cincinnati Financial Corporation [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Cost or amortized cost	4
Fair value	4
Balance sheet	4
Convertibles And Bonds With Warrants Attached [Member] | Fixed Maturities [Member] | Cincinnati Insurance Company [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Cost or amortized cost	27
Fair value	27
Balance sheet	27
United States Government [Member] | Fixed Maturities [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Cost or amortized cost	7
Fair value	8
Balance sheet	8
United States Government [Member] | Fixed Maturities [Member] | Cincinnati Casualty Company [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Cost or amortized cost	1
Fair value	2
Balance sheet	2
United States Government [Member] | Fixed Maturities [Member] | Cincinnati Indemnity Company [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Cost or amortized cost	1
Fair value	1
Balance sheet	1
United States Government [Member] | Fixed Maturities [Member] | Cincinnati Insurance Company [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Cost or amortized cost	1
Fair value	1
Balance sheet	1
United States Government [Member] | Fixed Maturities [Member] | Cincinnati Life Insurance Company [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Cost or amortized cost	4
Fair value	4
Balance sheet	4
Government-Sponsored Enterprises [Member] | Fixed Maturities [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Cost or amortized cost	164
Fair value	164
Balance sheet	164
Government-Sponsored Enterprises [Member] | Fixed Maturities [Member] | Cincinnati Life Insurance Company [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Cost or amortized cost	164
Fair value	164
Balance sheet	164
Foreign Government [Member] | Fixed Maturities [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Cost or amortized cost	3
Fair value	3
Balance sheet	3
Foreign Government [Member] | Fixed Maturities [Member] | Cincinnati Insurance Company [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Cost or amortized cost	3
Fair value	3
Balance sheet	3
Common Stock [Member] | Equity Securities [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Cost or amortized cost	2,270
Fair value	3,238
Balance sheet	3,238
Common Stock [Member] | Equity Securities [Member] | Cincinnati Financial Corporation [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Cost or amortized cost	728
Fair value	957
Balance sheet	957
Common Stock [Member] | Equity Securities [Member] | Cincinnati Casualty Company [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Cost or amortized cost	47
Fair value	68
Balance sheet	68
Common Stock [Member] | Equity Securities [Member] | Cincinnati Indemnity Company [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Cost or amortized cost	13
Fair value	16
Balance sheet	16
Common Stock [Member] | Equity Securities [Member] | Cincinnati Insurance Company [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Cost or amortized cost	1,432
Fair value	2,136
Balance sheet	2,136
Common Stock [Member] | Equity Securities [Member] | Cincinnati Life Insurance Company [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Cost or amortized cost	3
Fair value	4
Balance sheet	4
Common Stock [Member] | Equity Securities [Member] | CSU Producers Resources Inc. [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Cost or amortized cost	4
Fair value	5
Balance sheet	5
Common Stock [Member] | Equity Securities [Member] | Cincinnati Specialty Underwriters Insurance Company [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Cost or amortized cost	43
Fair value	52
Balance sheet	52
Nonredeemable Preferred Stock [Member] | Equity Securities [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Cost or amortized cost	99
Fair value	135
Balance sheet	135
Nonredeemable Preferred Stock [Member] | Equity Securities [Member] | Cincinnati Financial Corporation [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Cost or amortized cost	1
Fair value	1
Balance sheet	1
Nonredeemable Preferred Stock [Member] | Equity Securities [Member] | Cincinnati Insurance Company [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Cost or amortized cost	91
Fair value	121
Balance sheet	121
Nonredeemable Preferred Stock [Member] | Equity Securities [Member] | Cincinnati Life Insurance Company [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Cost or amortized cost	7
Fair value	13
Balance sheet	13
All Other Corporate Bonds [Member] | Fixed Maturities [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Cost or amortized cost	4,977
Fair value	5,598
Balance sheet	5,598
All Other Corporate Bonds [Member] | Fixed Maturities [Member] | Cincinnati Financial Corporation [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Cost or amortized cost	81
Fair value	99
Balance sheet	99
All Other Corporate Bonds [Member] | Fixed Maturities [Member] | Cincinnati Casualty Company [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Cost or amortized cost	96
Fair value	107
Balance sheet	107
All Other Corporate Bonds [Member] | Fixed Maturities [Member] | Cincinnati Indemnity Company [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Cost or amortized cost	22
Fair value	24
Balance sheet	24
All Other Corporate Bonds [Member] | Fixed Maturities [Member] | Cincinnati Insurance Company [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Cost or amortized cost	2,356
Fair value	2,664
Balance sheet	2,664
All Other Corporate Bonds [Member] | Fixed Maturities [Member] | Cincinnati Life Insurance Company [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Cost or amortized cost	2,285
Fair value	2,555
Balance sheet	2,555
All Other Corporate Bonds [Member] | Fixed Maturities [Member] | CSU Producers Resources Inc. [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Cost or amortized cost	6
Fair value	6
Balance sheet	6
All Other Corporate Bonds [Member] | Fixed Maturities [Member] | Cincinnati Specialty Underwriters Insurance Company [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Cost or amortized cost	131
Fair value	143
Balance sheet	143
Policy Loans [Member] | Other than Securities Investment [Member] | Cincinnati Life Insurance Company [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Cost or amortized cost	37
Balance sheet	37
Limited Partnership [Member] | Other than Securities Investment [Member] | Cincinnati Financial Corporation [Member]
Summary Of Investments Other Than Investments In Related Parties Reportable Data [Line Items]
Cost or amortized cost	31
Balance sheet	$ 31