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Employee Benefit Plans - Fair Value Measurements (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Other Postretirement Benefits Plan [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Increase (Decrease) for Actual Return (Loss) $ 122 $ (38)    
Defined Benefit Plan, Plan Assets, Payment for Settlement 0 0    
Defined Benefit Plan, Plan Assets, Amount 742 664 $ 736  
Other Postretirement Benefits Plan [Member] | Fair Value, Inputs, Level 1 [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 433 389    
Other Postretirement Benefits Plan [Member] | Fair Value, Inputs, Level 2 [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 135 120    
Other Postretirement Benefits Plan [Member] | Cash Equivalents [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 18 12    
Other Postretirement Benefits Plan [Member] | Cash Equivalents [Member] | Fair Value, Inputs, Level 1 [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 17 10 [1]    
Other Postretirement Benefits Plan [Member] | Cash Equivalents [Member] | Fair Value, Inputs, Level 2 [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 1 2 [1]    
Other Postretirement Benefits Plan [Member] | US Treasury Securities [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 23 13    
Other Postretirement Benefits Plan [Member] | US Treasury Securities [Member] | Fair Value, Inputs, Level 1 [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 23 13    
Other Postretirement Benefits Plan [Member] | US Treasury Securities [Member] | Fair Value, Inputs, Level 2 [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 0 0    
Other Postretirement Benefits Plan [Member] | Corporate Debt Securities [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 44 42    
Other Postretirement Benefits Plan [Member] | Corporate Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 0 0    
Other Postretirement Benefits Plan [Member] | Corporate Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 44 42    
Other Postretirement Benefits Plan [Member] | Municipal Bonds [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 57 45    
Other Postretirement Benefits Plan [Member] | Municipal Bonds [Member] | Fair Value, Inputs, Level 1 [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 0 0    
Other Postretirement Benefits Plan [Member] | Municipal Bonds [Member] | Fair Value, Inputs, Level 2 [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 57 45    
Other Postretirement Benefits Plan [Member] | US Government-sponsored Enterprises Debt Securities [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 33 30    
Other Postretirement Benefits Plan [Member] | US Government-sponsored Enterprises Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 0 0    
Other Postretirement Benefits Plan [Member] | US Government-sponsored Enterprises Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 33 30    
Other Postretirement Benefits Plan [Member] | Domestic Equity Securities [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 151 158    
Other Postretirement Benefits Plan [Member] | Domestic Equity Securities [Member] | Fair Value, Inputs, Level 1 [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 151 158 [1]    
Other Postretirement Benefits Plan [Member] | Domestic Equity Securities [Member] | Fair Value, Inputs, Level 2 [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 0 0 [1]    
Other Postretirement Benefits Plan [Member] | Foreign Equity Securities [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 6 6    
Other Postretirement Benefits Plan [Member] | Foreign Equity Securities [Member] | Fair Value, Inputs, Level 1 [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 6 6 [1]    
Other Postretirement Benefits Plan [Member] | Foreign Equity Securities [Member] | Fair Value, Inputs, Level 2 [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 0 0    
Other Postretirement Benefits Plan [Member] | Equity Funds [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount $ 236 $ 203    
Percentage of Investment Funds Comprised Of Equity Securitites 58.00% 65.00%    
Percentage of Investment Funds Comprised Of Debt Securities 42.00% 35.00%    
Percentage Of Investment Funds Invested in United States Securities 75.00% 79.00%    
Percentage Of Investment Funds Invested In International Securities 25.00% 21.00%    
Other Postretirement Benefits Plan [Member] | Equity Funds [Member] | Fair Value, Inputs, Level 1 [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount $ 236 $ 202    
Other Postretirement Benefits Plan [Member] | Equity Funds [Member] | Fair Value, Inputs, Level 2 [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 0 1    
Other Postretirement Benefits Plan [Member] | Plan Asset Categories Excluding Investments Measured with a NAV excluding the Practical Expedient [Domain]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 568 509    
Other Postretirement Benefits Plan [Member] | Accounting Standards Update 2015-07 [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 742 664    
Other Postretirement Benefits Plan [Member] | Accounting Standards Update 2015-07 [Member] | Equity Funds [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 169 149 [2]    
Other Postretirement Benefits Plan [Member] | Accounting Standards Update 2015-07 [Member] | Limited Partnership Interests [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 5 6    
UNITED STATES | Pension Plan [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Increase (Decrease) for Actual Return (Loss) 456 (147)    
Defined Benefit Plan, Plan Assets, Payment for Settlement (22) (119)    
Defined Benefit Plan, Plan Assets, Amount 2,656 2,396 2,761  
UNITED STATES | Pension Plan [Member] | Fair Value, Inputs, Level 1 [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 1,045 887    
UNITED STATES | Pension Plan [Member] | Fair Value, Inputs, Level 2 [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 561 572 [3]    
UNITED STATES | Pension Plan [Member] | Cash Equivalents [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 63 49    
UNITED STATES | Pension Plan [Member] | Cash Equivalents [Member] | Fair Value, Inputs, Level 1 [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 27 8    
UNITED STATES | Pension Plan [Member] | Cash Equivalents [Member] | Fair Value, Inputs, Level 2 [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 36 41    
UNITED STATES | Pension Plan [Member] | US Treasury Securities [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 210 160    
UNITED STATES | Pension Plan [Member] | US Treasury Securities [Member] | Fair Value, Inputs, Level 1 [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 210 160    
UNITED STATES | Pension Plan [Member] | US Treasury Securities [Member] | Fair Value, Inputs, Level 2 [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 0 0 [3]    
UNITED STATES | Pension Plan [Member] | Debt Security, Government, Non-US [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 5 5    
UNITED STATES | Pension Plan [Member] | Debt Security, Government, Non-US [Member] | Fair Value, Inputs, Level 1 [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 0 0    
UNITED STATES | Pension Plan [Member] | Debt Security, Government, Non-US [Member] | Fair Value, Inputs, Level 2 [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 5 5 [3]    
UNITED STATES | Pension Plan [Member] | Corporate Debt Securities [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 376 373    
UNITED STATES | Pension Plan [Member] | Corporate Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 0 0 [3]    
UNITED STATES | Pension Plan [Member] | Corporate Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 376 373 [3]    
UNITED STATES | Pension Plan [Member] | Municipal Bonds [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 28 29    
UNITED STATES | Pension Plan [Member] | Municipal Bonds [Member] | Fair Value, Inputs, Level 1 [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 0 0 [3]    
UNITED STATES | Pension Plan [Member] | Municipal Bonds [Member] | Fair Value, Inputs, Level 2 [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 28 29    
UNITED STATES | Pension Plan [Member] | US Government-sponsored Enterprises Debt Securities [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 115 123    
UNITED STATES | Pension Plan [Member] | US Government-sponsored Enterprises Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 0 0    
UNITED STATES | Pension Plan [Member] | US Government-sponsored Enterprises Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 115 123    
UNITED STATES | Pension Plan [Member] | Domestic Equity Securities [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 548 493    
UNITED STATES | Pension Plan [Member] | Domestic Equity Securities [Member] | Fair Value, Inputs, Level 1 [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 547 492 [3]    
UNITED STATES | Pension Plan [Member] | Domestic Equity Securities [Member] | Fair Value, Inputs, Level 2 [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 1 1 [3]    
UNITED STATES | Pension Plan [Member] | Foreign Equity Securities [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 136 108    
UNITED STATES | Pension Plan [Member] | Foreign Equity Securities [Member] | Fair Value, Inputs, Level 1 [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 136 108    
UNITED STATES | Pension Plan [Member] | Foreign Equity Securities [Member] | Fair Value, Inputs, Level 2 [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 0 0 [3]    
UNITED STATES | Pension Plan [Member] | Equity Funds [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount $ 125 $ 119 [4]    
Percentage of Investment Funds Comprised Of Equity Securitites 62.00% 59.00%    
Percentage of Investment Funds Comprised Of Debt Securities 38.00% 41.00%    
Percentage Of Investment Funds Invested in United States Securities 66.00% 73.00%    
Percentage Of Investment Funds Invested In International Securities 34.00% 27.00%    
UNITED STATES | Pension Plan [Member] | Equity Funds [Member] | Fair Value, Inputs, Level 1 [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount $ 125 $ 119 [3],[4]    
UNITED STATES | Pension Plan [Member] | Equity Funds [Member] | Fair Value, Inputs, Level 2 [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 0 0    
UNITED STATES | Pension Plan [Member] | Plan Asset Categories Excluding Investments Measured with a NAV excluding the Practical Expedient [Domain]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 1,606 1,459    
UNITED STATES | Pension Plan [Member] | Accounting Standards Update 2015-07 [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 2,656 2,396    
UNITED STATES | Pension Plan [Member] | Accounting Standards Update 2015-07 [Member] | Equity Funds [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 915 792 [4]    
UNITED STATES | Pension Plan [Member] | Accounting Standards Update 2015-07 [Member] | Limited Partnership Interests [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 93 104 [5]    
UNITED STATES | Pension Plan [Member] | Accounting Standards Update 2015-07 [Member] | Real Estate Funds [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 42 41    
UNITED KINGDOM | Pension Plan [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Increase (Decrease) for Actual Return (Loss) 194 (44)    
Defined Benefit Plan, Plan Assets, Payment for Settlement (99) (205)    
Defined Benefit Plan, Plan Assets, Amount 2,151 1,989 2,368  
Defined Benefit Plan, Plan Assets, Foreign Currency Translation Gain (Loss) 81 120    
UNITED KINGDOM | Pension Plan [Member] | Fair Value, Inputs, Level 1 [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount [6] 963 894    
UNITED KINGDOM | Pension Plan [Member] | Fair Value, Inputs, Level 2 [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 842 756    
UNITED KINGDOM | Pension Plan [Member] | Fair Value, Inputs, Level 3 [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount [6] 243 239    
UNITED KINGDOM | Pension Plan [Member] | Cash Equivalents [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 27 62    
UNITED KINGDOM | Pension Plan [Member] | Cash Equivalents [Member] | Fair Value, Inputs, Level 1 [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 3 3 [6]    
UNITED KINGDOM | Pension Plan [Member] | Cash Equivalents [Member] | Fair Value, Inputs, Level 2 [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount [6] 24 59    
UNITED KINGDOM | Pension Plan [Member] | Cash Equivalents [Member] | Fair Value, Inputs, Level 3 [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount [6] 0 0    
UNITED KINGDOM | Pension Plan [Member] | United Kingdom Government Obligations [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 960 891    
UNITED KINGDOM | Pension Plan [Member] | United Kingdom Government Obligations [Member] | Fair Value, Inputs, Level 1 [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 960 891    
UNITED KINGDOM | Pension Plan [Member] | United Kingdom Government Obligations [Member] | Fair Value, Inputs, Level 2 [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 0 [6] 0    
UNITED KINGDOM | Pension Plan [Member] | United Kingdom Government Obligations [Member] | Fair Value, Inputs, Level 3 [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 0 0    
UNITED KINGDOM | Pension Plan [Member] | Equity Funds [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount [7] $ 818 $ 697    
Percentage of Investment Funds Comprised Of Equity Securitites 38.00% 36.00%    
Percentage of Investment Funds Comprised Of Debt Securities 62.00% 64.00%    
UNITED KINGDOM | Pension Plan [Member] | Equity Funds [Member] | Fair Value, Inputs, Level 1 [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount [6],[7] $ 0 $ 0    
UNITED KINGDOM | Pension Plan [Member] | Equity Funds [Member] | Fair Value, Inputs, Level 2 [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 818 697    
UNITED KINGDOM | Pension Plan [Member] | Equity Funds [Member] | Fair Value, Inputs, Level 3 [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 0 0 [6],[7]    
UNITED KINGDOM | Pension Plan [Member] | Real Estate Funds [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 243 239    
UNITED KINGDOM | Pension Plan [Member] | Real Estate Funds [Member] | Fair Value, Inputs, Level 1 [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 0 0    
UNITED KINGDOM | Pension Plan [Member] | Real Estate Funds [Member] | Fair Value, Inputs, Level 2 [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 0 0    
UNITED KINGDOM | Pension Plan [Member] | Real Estate Funds [Member] | Fair Value, Inputs, Level 3 [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 243 [6] 239 [6] 230 $ 105
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Actual Return (Loss) on Plan Assets Still Held (5) 23 6  
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Increase (Decrease) for Purchase, Sale, and Settlement 0 0 104  
Defined Benefit Plan, Plan Assets, Foreign Currency Translation Gain (Loss) 9 (14) $ 15  
UNITED KINGDOM | Pension Plan [Member] | Plan Asset Categories Excluding Investments Measured with a NAV excluding the Practical Expedient [Domain]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 2,048 1,889    
UNITED KINGDOM | Pension Plan [Member] | Accounting Standards Update 2015-07 [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount 2,151 1,989    
UNITED KINGDOM | Pension Plan [Member] | Accounting Standards Update 2015-07 [Member] | Equity Funds [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets, Amount [7] $ 103 $ 100    
[1] Refer to Note 15 for additional discussion regarding the three levels of the fair value hierarchy.
[2] Investment funds are comprised of mutual funds and collective trust funds. These funds consist of equity and debt securities of approximately 58% and 42%, respectively, for 2019 and 65% and 35%, respectively, for 2018. Additionally, these funds are invested in United States and international securities of approximately 75% and 25%, respectively, for 2019 and 79% and 21%, respectively, for 2018.
[3] Refer to Note 15 for additional discussion regarding the three levels of the fair value hierarchy.
[4] Investment funds are comprised of mutual funds and collective trust funds. These funds consist of equity and debt securities of approximately 62% and 38%, respectively, for 2019 and 59% and 41%, respectively, for 2018. Additionally, these funds are invested in United States and international securities of approximately 66% and 34%, respectively, for 2019 and 73% and 27%, respectively, for 2018.
[5] Limited partnership interests include several funds that invest primarily in real estate, buyout, growth equity and venture capital.
[6] Refer to Note 15 for additional discussion regarding the three levels of the fair value hierarchy.
[7] Investment funds are comprised of mutual funds and collective trust funds. These funds consist of equity and debt securities of approximately 38% and 62%, respectively, for 2019 and 36% and 64%, respectively, for 2018.