Investments - Investments - Available-for-Sale Securities (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, available-for-sale, at fair value, amortized cost	$ 39,473	$ 40,078
Allowance for credit losses, fixed maturity, AFS	(12)	0
Gross Unrealized Gains, fixed maturities, available-for-sale	1,699	2,125
Gross Unrealized Losses, fixed maturities, available-for-sale	(955)	(55)
Fixed maturities, available-for-sale, at fair value (amortized cost of $54,478 and $53,805)	40,205	42,148
Accumulated Other Comprehensive Income (Loss), Other than Temporary Impairment, Not Credit Loss, Net of Tax, Available-for-sale, Debt Securities		4
Amortized Cost
One year or less	1,197	1,082
Over one year through five years	7,477	7,200
Over five years through ten years	7,032	7,395
Over ten years	11,863	11,769
Subtotal	27,569	27,446
Mortgage-backed and asset-backed securities	11,904	12,632
Fair Value
One year or less	1,196	1,090
Over one year through five years	7,447	7,401
Over five years through ten years	7,053	7,803
Over ten years	12,784	12,988
Subtotal	28,480	29,282
Mortgage-backed and asset-backed securities	11,725	12,866
ABS
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, available-for-sale, at fair value, amortized cost	1,368	1,461
Allowance for credit losses, fixed maturity, AFS	0
Gross Unrealized Gains, fixed maturities, available-for-sale	6	18
Gross Unrealized Losses, fixed maturities, available-for-sale	(26)	(3)
Fixed maturities, available-for-sale, at fair value (amortized cost of $54,478 and $53,805)	1,348	1,476
Accumulated Other Comprehensive Income (Loss), Other than Temporary Impairment, Not Credit Loss, Net of Tax, Available-for-sale, Debt Securities		0
CLOs
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, available-for-sale, at fair value, amortized cost	2,168	2,186
Allowance for credit losses, fixed maturity, AFS	0
Gross Unrealized Gains, fixed maturities, available-for-sale	0	5
Gross Unrealized Losses, fixed maturities, available-for-sale	(179)	(8)
Fixed maturities, available-for-sale, at fair value (amortized cost of $54,478 and $53,805)	1,989	2,183
Accumulated Other Comprehensive Income (Loss), Other than Temporary Impairment, Not Credit Loss, Net of Tax, Available-for-sale, Debt Securities		0
CMBS
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, available-for-sale, at fair value, amortized cost	4,316	4,210
Allowance for credit losses, fixed maturity, AFS	0
Gross Unrealized Gains, fixed maturities, available-for-sale	102	141
Gross Unrealized Losses, fixed maturities, available-for-sale	(116)	(13)
Fixed maturities, available-for-sale, at fair value (amortized cost of $54,478 and $53,805)	4,302	4,338
Accumulated Other Comprehensive Income (Loss), Other than Temporary Impairment, Not Credit Loss, Net of Tax, Available-for-sale, Debt Securities		4
Corporate
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, available-for-sale, at fair value, amortized cost	16,744	16,435
Allowance for credit losses, fixed maturity, AFS	12	0
Gross Unrealized Gains, fixed maturities, available-for-sale	585	986
Gross Unrealized Losses, fixed maturities, available-for-sale	(519)	(25)
Fixed maturities, available-for-sale, at fair value (amortized cost of $54,478 and $53,805)	16,798	17,396
Accumulated Other Comprehensive Income (Loss), Other than Temporary Impairment, Not Credit Loss, Net of Tax, Available-for-sale, Debt Securities		0
Foreign Govt./Govt. Agencies
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, available-for-sale, at fair value, amortized cost	1,058	1,057
Allowance for credit losses, fixed maturity, AFS	0
Gross Unrealized Gains, fixed maturities, available-for-sale	28	66
Gross Unrealized Losses, fixed maturities, available-for-sale	(23)	0
Fixed maturities, available-for-sale, at fair value (amortized cost of $54,478 and $53,805)	1,063	1,123
Accumulated Other Comprehensive Income (Loss), Other than Temporary Impairment, Not Credit Loss, Net of Tax, Available-for-sale, Debt Securities		0
Municipal
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, available-for-sale, at fair value, amortized cost	8,843	8,763
Allowance for credit losses, fixed maturity, AFS	0
Gross Unrealized Gains, fixed maturities, available-for-sale	684	737
Gross Unrealized Losses, fixed maturities, available-for-sale	(30)	(2)
Fixed maturities, available-for-sale, at fair value (amortized cost of $54,478 and $53,805)	9,497	9,498
Accumulated Other Comprehensive Income (Loss), Other than Temporary Impairment, Not Credit Loss, Net of Tax, Available-for-sale, Debt Securities		0
RMBS
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, available-for-sale, at fair value, amortized cost	4,052	4,775
Allowance for credit losses, fixed maturity, AFS	0
Gross Unrealized Gains, fixed maturities, available-for-sale	96	97
Gross Unrealized Losses, fixed maturities, available-for-sale	(62)	(3)
Fixed maturities, available-for-sale, at fair value (amortized cost of $54,478 and $53,805)	4,086	4,869
Accumulated Other Comprehensive Income (Loss), Other than Temporary Impairment, Not Credit Loss, Net of Tax, Available-for-sale, Debt Securities		0
U.S. Treasuries
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, available-for-sale, at fair value, amortized cost	924	1,191
Allowance for credit losses, fixed maturity, AFS	0
Gross Unrealized Gains, fixed maturities, available-for-sale	198	75
Gross Unrealized Losses, fixed maturities, available-for-sale	0	(1)
Fixed maturities, available-for-sale, at fair value (amortized cost of $54,478 and $53,805)	$ 1,122	1,265
Accumulated Other Comprehensive Income (Loss), Other than Temporary Impairment, Not Credit Loss, Net of Tax, Available-for-sale, Debt Securities		$ 0