Fair Value Measurements - Fair Values of Separate Account Assets (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Guaranteed separate accounts	$ 523
Guaranteed separate accounts		$ 490
Non-guaranteed separate accounts	7,880
Non-guaranteed separate accounts		7,235
Subtotal	8,403
Subtotal		7,725
Non-guaranteed separate accounts priced at NAV as a practical expedient	683
Non-guaranteed separate accounts priced at NAV as a practical expedient		756
Total		8,481
Separate account assets of business classified as held for sale		(16)
Separate account assets per Consolidated Balance Sheets	9,086	8,465
Pension Plan
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-guaranteed separate accounts	4,200
Non-guaranteed separate accounts		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	226
Guaranteed separate accounts		219
Non-guaranteed separate accounts	1,925
Non-guaranteed separate accounts		1,450
Subtotal	2,151
Subtotal		1,669
Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Guaranteed separate accounts	297
Guaranteed separate accounts		271
Non-guaranteed separate accounts	5,600
Non-guaranteed separate accounts		5,522
Subtotal	5,897
Subtotal		5,793
Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Guaranteed separate accounts	0
Guaranteed separate accounts		0
Non-guaranteed separate accounts	355
Non-guaranteed separate accounts		263
Subtotal	355
Subtotal		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	$ 300
Non-guaranteed separate accounts		$ 200