Fair Value Measurements - Changes in Unrealized Gains (Losses) Included in Net Income for Financial Instruments Classified as Level 3 Still Held at Year End (Details) - Fair Value, Recurring [Member] - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Unrealized Gain/(Loss) Included in Net Income, Assets	$ (3)	$ (4)	$ (9)	$ (8)
Other Comprehensive Income (Loss) [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Unrealized Gain/(Loss) Included in Net Income, Assets	78	2	(25)	8
Significant Unobservable Inputs (Level 3)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Unrealized Gain/(Loss) Included in Net Income, Liabilities	0	(2)	12	(6)
Significant Unobservable Inputs (Level 3) | Contingent Consideration
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Unrealized Gain/(Loss) Included in Net Income, Liabilities	0	(2)	12	(6)
Significant Unobservable Inputs (Level 3) | Other Comprehensive Income (Loss) [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Unrealized Gain/(Loss) Included in Net Income, Liabilities	0	0	0	0
Significant Unobservable Inputs (Level 3) | Other Comprehensive Income (Loss) [Member] | Contingent Consideration
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Unrealized Gain/(Loss) Included in Net Income, Liabilities	0	0	0	0
Significant Unobservable Inputs (Level 3) | Equity Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Unrealized Gain/(Loss) Included in Net Income, Assets	(3)	0	(9)	0
Significant Unobservable Inputs (Level 3) | Equity Securities [Member] | Other Comprehensive Income (Loss) [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Unrealized Gain/(Loss) Included in Net Income, Assets	0	0	0	0
Significant Unobservable Inputs (Level 3) | Freestanding Derivatives, net
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Unrealized Gain/(Loss) Included in Net Income, Derivatives	0	(4)	0	(7)
Significant Unobservable Inputs (Level 3) | Freestanding Derivatives, net | Equity
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Unrealized Gain/(Loss) Included in Net Income, Derivatives	0	(4)	0	(6)
Significant Unobservable Inputs (Level 3) | Freestanding Derivatives, net | Interest rate derivatives
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Unrealized Gain/(Loss) Included in Net Income, Derivatives	0	0	0	(1)
Significant Unobservable Inputs (Level 3) | Freestanding Derivatives, net | Other Comprehensive Income (Loss) [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Unrealized Gain/(Loss) Included in Net Income, Derivatives	0	0	0	0
Significant Unobservable Inputs (Level 3) | Freestanding Derivatives, net | Other Comprehensive Income (Loss) [Member] | Equity
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Unrealized Gain/(Loss) Included in Net Income, Derivatives		0	0	0
Significant Unobservable Inputs (Level 3) | Freestanding Derivatives, net | Other Comprehensive Income (Loss) [Member] | Interest rate derivatives
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Unrealized Gain/(Loss) Included in Net Income, Derivatives	0	0	0	0
Significant Unobservable Inputs (Level 3) | Total Fixed Maturities, AFS | Securities available-for-sale and other
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Unrealized Gain/(Loss) Included in Net Income, Assets	0	0	0	(1)
Significant Unobservable Inputs (Level 3) | Total Fixed Maturities, AFS | Securities available-for-sale and other | Other Comprehensive Income (Loss) [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Unrealized Gain/(Loss) Included in Net Income, Assets	78	2	(25)	8
Significant Unobservable Inputs (Level 3) | Total Fixed Maturities, AFS | Collateralized loan obligations (CLOs) | Securities available-for-sale and other
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Unrealized Gain/(Loss) Included in Net Income, Assets	0	0	0	0
Significant Unobservable Inputs (Level 3) | Total Fixed Maturities, AFS | Collateralized loan obligations (CLOs) | Securities available-for-sale and other | Other Comprehensive Income (Loss) [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Unrealized Gain/(Loss) Included in Net Income, Assets	4	0	(2)	0
Significant Unobservable Inputs (Level 3) | Total Fixed Maturities, AFS | Corporate | Securities available-for-sale and other
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Unrealized Gain/(Loss) Included in Net Income, Assets	0	0	0	(1)
Significant Unobservable Inputs (Level 3) | Total Fixed Maturities, AFS | Corporate | Securities available-for-sale and other | Other Comprehensive Income (Loss) [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Unrealized Gain/(Loss) Included in Net Income, Assets	61	2	(12)	9
Significant Unobservable Inputs (Level 3) | Total Fixed Maturities, AFS | RMBS | Securities available-for-sale and other
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Unrealized Gain/(Loss) Included in Net Income, Assets	0	0	0	0
Significant Unobservable Inputs (Level 3) | Total Fixed Maturities, AFS | RMBS | Securities available-for-sale and other | Other Comprehensive Income (Loss) [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Changes in Unrealized Gain/(Loss) Included in Net Income, Assets	$ 13	$ 0	$ (11)	$ (1)