Fair Value Measurements - Fair Values of Separate Account Assets (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Guaranteed separate accounts	$ 510	$ 490
Non-guaranteed separate accounts, including disposal groups	7,384	7,235
Subtotal	7,894	7,725
Non-guaranteed separate accounts priced at NAV as a practical expedient	736	756
Total	8,630	8,481
Separate account assets of business classified as held for sale	(14)	(16)
Separate account assets per Consolidated Balance Sheets	8,616	8,465
Pension Plan
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-guaranteed separate accounts, including disposal groups	3,900	4,000
Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Guaranteed separate accounts	208	219
Non-guaranteed separate accounts, including disposal groups	1,541	1,450
Subtotal	1,749	1,669
Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Guaranteed separate accounts	302	271
Non-guaranteed separate accounts, including disposal groups	5,508	5,522
Subtotal	5,810	5,793
Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Guaranteed separate accounts	0	0
Non-guaranteed separate accounts, including disposal groups	335	263
Subtotal	335	263
Significant Unobservable Inputs (Level 3) | Pension Plan
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-guaranteed separate accounts, including disposal groups	$ 300	$ 200