Investments - Available-for-Sale Securities (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Fixed maturities, available-for-sale, at fair value, amortized cost	$ 20,515	$ 20,914
Gross Unrealized Gains, fixed maturities, available-for-sale	1,458	1,958
Gross Unrealized Losses, fixed maturities, available-for-sale	(192)	(73)
Available-for-sale Securities, Debt Securities	21,781	22,799
Non-Credit OTTI	(1)	(1)
Equity securities, available-for-sale, Cost or Amortized Cost		140
Equity securities, available-for-sale, at fair value (cost of $0 and $140)	0	154
Available-for-sale, Cost or Amortized Cost	20,515	21,054
Available-for-sale, Gross Unrealized Gains	1,458	1,972
Available-for-sale, Gross Unrealized Losses	(192)	(73)
Available-for-sale, Fair Value	21,781	22,953
Amortized Cost
One year or less	914	844
Over one year through five years	3,418	3,498
Over five years through ten years	3,005	3,178
Over ten years	8,242	8,238
Subtotal	15,579	15,758
Mortgage-backed and asset-backed securities	4,936	5,156
Fair Value
One year or less	918	850
Over one year through five years	3,454	3,580
Over five years through ten years	3,063	3,321
Over ten years	9,398	9,830
Subtotal	16,833	17,581
Mortgage-backed and asset-backed securities	4,948	5,218
ABS [Member]
Schedule of Available-for-sale Securities [Line Items]
Fixed maturities, available-for-sale, at fair value, amortized cost	831	821
Gross Unrealized Gains, fixed maturities, available-for-sale	8	9
Gross Unrealized Losses, fixed maturities, available-for-sale	(10)	(11)
Available-for-sale Securities, Debt Securities	829	819
Non-Credit OTTI	0	0
CDOs
Schedule of Available-for-sale Securities [Line Items]
Fixed maturities, available-for-sale, at fair value, amortized cost	782	886
Gross Unrealized Gains, fixed maturities, available-for-sale	0	2
Gross Unrealized Losses, fixed maturities, available-for-sale	(2)	0
Available-for-sale Securities, Debt Securities	780	888
Non-Credit OTTI	0	0
CMBS
Schedule of Available-for-sale Securities [Line Items]
Fixed maturities, available-for-sale, at fair value, amortized cost	1,996	2,061
Gross Unrealized Gains, fixed maturities, available-for-sale	30	45
Gross Unrealized Losses, fixed maturities, available-for-sale	(39)	(22)
Available-for-sale Securities, Debt Securities	1,987	2,084
Non-Credit OTTI	(1)	(1)
Corporate
Schedule of Available-for-sale Securities [Line Items]
Fixed maturities, available-for-sale, at fair value, amortized cost	12,444	12,587
Gross Unrealized Gains, fixed maturities, available-for-sale	1,093	1,483
Gross Unrealized Losses, fixed maturities, available-for-sale	(113)	(32)
Available-for-sale Securities, Debt Securities	13,424	14,038
Non-Credit OTTI	0	0
Foreign government/government agencies
Schedule of Available-for-sale Securities [Line Items]
Fixed maturities, available-for-sale, at fair value, amortized cost	399	379
Gross Unrealized Gains, fixed maturities, available-for-sale	22	30
Gross Unrealized Losses, fixed maturities, available-for-sale	(6)	(2)
Available-for-sale Securities, Debt Securities	415	407
Non-Credit OTTI	0	0
Municipal
Schedule of Available-for-sale Securities [Line Items]
Fixed maturities, available-for-sale, at fair value, amortized cost	1,126	1,125
Gross Unrealized Gains, fixed maturities, available-for-sale	114	142
Gross Unrealized Losses, fixed maturities, available-for-sale	(2)	(1)
Available-for-sale Securities, Debt Securities	1,238	1,266
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	1,610	1,667
Gross Unrealized Gains, fixed maturities, available-for-sale	157	206
Gross Unrealized Losses, fixed maturities, available-for-sale	(11)	(3)
Available-for-sale Securities, Debt Securities	1,756	1,870
Non-Credit OTTI	0	0
RMBS
Schedule of Available-for-sale Securities [Line Items]
Fixed maturities, available-for-sale, at fair value, amortized cost	1,327	1,388
Gross Unrealized Gains, fixed maturities, available-for-sale	34	41
Gross Unrealized Losses, fixed maturities, available-for-sale	(9)	(2)
Available-for-sale Securities, Debt Securities	1,352	1,427
Non-Credit OTTI	0	0
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Non-Credit OTTI		0
Equity securities, available-for-sale, Cost or Amortized Cost		140
Gross Unrealized Gains, fixed maturities, available-for-sale		14
Gross Unrealized Losses Gains, fixed maturities, available-for-sale		0
Equity securities, available-for-sale, at fair value (cost of $0 and $140)	$ 154	$ 154