Investments - Investments - Available-for-Sale Securities (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Fixed maturities, available-for-sale, at fair value, amortized cost	$ 35,913	$ 35,612
Gross Unrealized Gains, fixed maturities, available-for-sale	831	1,466
Gross Unrealized Losses, fixed maturities, available-for-sale	(550)	(114)
Fixed maturities, available-for-sale, at fair value (amortized cost of $54,478 and $53,805)	36,194	36,964
Non-Credit OTTI	(4)	(5)
Equity securities, available-for-sale, Cost or Amortized Cost	0	907
Equity securities, AFS	0	1,012
Available-for-sale, Cost or Amortized Cost	35,913	36,519
Available-for-sale, Gross Unrealized Gains	831	1,587
Available-for-sale, Gross Unrealized Losses	(550)	(130)
Available-for-sale, Fair Value	36,194	37,976
Amortized Cost
One year or less	1,321	1,507
Over one year through five years	5,955	5,007
Over five years through ten years	6,614	6,505
Over ten years	13,203	13,928
Subtotal	27,093	26,947
Mortgage-backed and asset-backed securities	8,820	8,665
Fair Value
One year or less	1,326	1,513
Over one year through five years	5,980	5,119
Over five years through ten years	6,546	6,700
Over ten years	13,558	14,866
Subtotal	27,410	28,198
Mortgage-backed and asset-backed securities	8,784	8,766
ABS
Schedule of Available-for-sale Securities [Line Items]
Fixed maturities, available-for-sale, at fair value, amortized cost	993	1,119
Gross Unrealized Gains, fixed maturities, available-for-sale	4	9
Gross Unrealized Losses, fixed maturities, available-for-sale	(3)	(2)
Fixed maturities, available-for-sale, at fair value (amortized cost of $54,478 and $53,805)	994	1,126
Non-Credit OTTI	0	0
CDOs
Schedule of Available-for-sale Securities [Line Items]
Fixed maturities, available-for-sale, at fair value, amortized cost	1,091	1,257
Gross Unrealized Gains, fixed maturities, available-for-sale	1	3
Gross Unrealized Losses, fixed maturities, available-for-sale	(3)	0
Fixed maturities, available-for-sale, at fair value (amortized cost of $54,478 and $53,805)	1,089	1,260
Non-Credit OTTI	0	0
CMBS
Schedule of Available-for-sale Securities [Line Items]
Fixed maturities, available-for-sale, at fair value, amortized cost	3,536	3,304
Gross Unrealized Gains, fixed maturities, available-for-sale	31	58
Gross Unrealized Losses, fixed maturities, available-for-sale	(73)	(26)
Fixed maturities, available-for-sale, at fair value (amortized cost of $54,478 and $53,805)	3,494	3,336
Non-Credit OTTI	(4)	(5)
Corporate
Schedule of Available-for-sale Securities [Line Items]
Fixed maturities, available-for-sale, at fair value, amortized cost	13,493	12,370
Gross Unrealized Gains, fixed maturities, available-for-sale	192	490
Gross Unrealized Losses, fixed maturities, available-for-sale	(336)	(56)
Fixed maturities, available-for-sale, at fair value (amortized cost of $54,478 and $53,805)	13,349	12,804
Non-Credit OTTI	0	0
Foreign Govt./Govt. Agencies
Schedule of Available-for-sale Securities [Line Items]
Fixed maturities, available-for-sale, at fair value, amortized cost	1,149	1,071
Gross Unrealized Gains, fixed maturities, available-for-sale	12	43
Gross Unrealized Losses, fixed maturities, available-for-sale	(28)	(4)
Fixed maturities, available-for-sale, at fair value (amortized cost of $54,478 and $53,805)	1,133	1,110
Non-Credit OTTI	0	0
Municipal
Schedule of Available-for-sale Securities [Line Items]
Fixed maturities, available-for-sale, at fair value, amortized cost	10,678	11,743
Gross Unrealized Gains, fixed maturities, available-for-sale	508	754
Gross Unrealized Losses, fixed maturities, available-for-sale	(44)	(12)
Fixed maturities, available-for-sale, at fair value (amortized cost of $54,478 and $53,805)	11,142	12,485
Non-Credit OTTI	0	0
RMBS
Schedule of Available-for-sale Securities [Line Items]
Fixed maturities, available-for-sale, at fair value, amortized cost	3,200	2,985
Gross Unrealized Gains, fixed maturities, available-for-sale	48	63
Gross Unrealized Losses, fixed maturities, available-for-sale	(41)	(4)
Fixed maturities, available-for-sale, at fair value (amortized cost of $54,478 and $53,805)	3,207	3,044
Non-Credit OTTI	0	0
U.S. Treasuries
Schedule of Available-for-sale Securities [Line Items]
Fixed maturities, available-for-sale, at fair value, amortized cost	1,773	1,763
Gross Unrealized Gains, fixed maturities, available-for-sale	35	46
Gross Unrealized Losses, fixed maturities, available-for-sale	(22)	(10)
Fixed maturities, available-for-sale, at fair value (amortized cost of $54,478 and $53,805)	1,786	1,799
Non-Credit OTTI	0	0
Equity Securities, at fair value
Schedule of Available-for-sale Securities [Line Items]
Non-Credit OTTI		0
Equity securities, available-for-sale, Cost or Amortized Cost		907
Gross Unrealized Gains, fixed maturities, available-for-sale		121
Gross Unrealized Losses Gains, fixed maturities, available-for-sale		(16)
Equity securities, AFS		$ 1,012