Fair Value (Unobservable Input Reconciliation) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Net Derivatives
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	$ 27	$ 7	$ 27	$ 157
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance, beginning of period	(288)	51	(562)	(179)
Total realized/unrealized gains (losses) included in net income (loss)	33	(3)	47	185
Total realized/unrealized gains (losses) included in AOCI	4	(8)	144	28
Purchases	0	0	0	6
Sales	0	0	0	0
Issuances	0	(1)	(7)	(1)
Settlements	(12)	(21)	115	(19)
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	(2)
Balance, end of period	(263)	18	(263)	18
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	27	7	27	157
Net Embedded Derivatives
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	204	227	422	(1,469)
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance, beginning of period	(1,388)	(2,751)	(1,411)	(675)
Total realized/unrealized gains (losses) included in net income (loss)	222	262	444	(1,450)
Total realized/unrealized gains (losses) included in AOCI	4	(27)	(42)	(239)
Purchases	0	0	0	0
Sales	0	0	0	0
Issuances	0	0	0	0
Settlements	(92)	(84)	(245)	(236)
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Balance, end of period	(1,254)	(2,600)	(1,254)	(2,600)
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	204	227	422	(1,469)
Residential mortgage loans — FVO
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	615	449	566	314
Total realized/unrealized gains (losses) included in net income (loss)	32	10	38	22
Total realized/unrealized gains (losses) included in AOCI	0	0	0	0
Purchases	10	42	184	187
Sales	(72)	(5)	(155)	(12)
Issuances	0	0	0	0
Settlements	(21)	(15)	(69)	(30)
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Balance, end of period	564	481	564	481
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	32	10	38	22
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	32	10	38	22
Corporate fixed maturity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	11,632	10,938	11,537	10,311
Total realized/unrealized gains (losses) included in net income (loss)	(3)	8	6	(4)
Total realized/unrealized gains (losses) included in AOCI	164	96	612	846
Purchases	713	588	2,802	1,650
Sales	(285)	(414)	(1,487)	(811)
Issuances	0	0	0	0
Settlements	0	0	0	0
Transfers into Level 3	123	373	83	473
Transfers out of Level 3	(226)	(202)	(1,435)	(1,078)
Balance, end of period	12,118	11,387	12,118	11,387
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	(2)	0	6	0
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	(2)	0	6	0
Foreign government
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	208	367	289	829
Total realized/unrealized gains (losses) included in net income (loss)	1	2	3	10
Total realized/unrealized gains (losses) included in AOCI	(2)	2	4	(2)
Purchases	0	21	7	58
Sales	0	(7)	(97)	(36)
Issuances	0	0	0	0
Settlements	0	0	0	0
Transfers into Level 3	0	0	0	41
Transfers out of Level 3	(9)	(62)	(8)	(577)
Balance, end of period	198	323	198	323
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	1	2	3	9
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	1	2	3	9
U.S. government and agency
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	0	297	0	0
Total realized/unrealized gains (losses) included in net income (loss)	0	0	0	0
Total realized/unrealized gains (losses) included in AOCI	0	(1)	0	14
Purchases	0	100	0	111
Sales	0	0	0	0
Issuances	0	0	0	0
Settlements	0	0	0	0
Transfers into Level 3	0	0	0	181
Transfers out of Level 3	0	(101)	0	(11)
Balance, end of period	0	295	0	295
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	0	0	0	0
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	0	0	0	0
Structured Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	4,939	4,862	5,215	5,121
Total realized/unrealized gains (losses) included in net income (loss)	13	26	80	74
Total realized/unrealized gains (losses) included in AOCI	31	25	118	33
Purchases	468	918	867	2,004
Sales	(478)	(367)	(1,329)	(1,182)
Issuances	0	0	0	0
Settlements	0	0	0	0
Transfers into Level 3	0	44	10	26
Transfers out of Level 3	(440)	(236)	(428)	(804)
Balance, end of period	4,533	5,272	4,533	5,272
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	22	26	68	75
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	22	26	68	75
State and political subdivision
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	0	45	10	34
Total realized/unrealized gains (losses) included in net income (loss)	0	0	0	1
Total realized/unrealized gains (losses) included in AOCI	0	3	2	1
Purchases	0	0	0	0
Sales	(1)	0	0	0
Issuances	0	0	0	0
Settlements	0	0	0	0
Transfers into Level 3	62	7	59	7
Transfers out of Level 3	0	(17)	(10)	(5)
Balance, end of period	61	38	61	38
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	0	0	0	1
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	0	0	0	1
Equity Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	468	509	468	334
Total realized/unrealized gains (losses) included in net income (loss)	(1)	4	(14)	(22)
Total realized/unrealized gains (losses) included in AOCI	(4)	(12)	30	41
Purchases	13	4	18	20
Sales	(52)	(11)	(74)	(16)
Issuances	0	0	0	0
Settlements	0	0	0	0
Transfers into Level 3	0	1	0	327
Transfers out of Level 3	0	(6)	(4)	(195)
Balance, end of period	424	489	424	489
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	(2)	0	(12)	(26)
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	(2)	0	(12)	(26)
FVO Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	312	231	287	270
Total realized/unrealized gains (losses) included in net income (loss)	7	4	20	9
Total realized/unrealized gains (losses) included in AOCI	0	0	0	0
Purchases	73	18	209	43
Sales	(70)	(6)	(115)	(29)
Issuances	0	0	0	0
Settlements	0	0	0	0
Transfers into Level 3	3	0	3	18
Transfers out of Level 3	(21)	(4)	(100)	(68)
Balance, end of period	304	243	304	243
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	7	4	16	9
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	7	4	16	9
Short-term Investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	822	64	46	244
Total realized/unrealized gains (losses) included in net income (loss)	0	1	0	1
Total realized/unrealized gains (losses) included in AOCI	0	(1)	0	4
Purchases	1	222	401	231
Sales	(247)	(55)	(2)	(247)
Issuances	0	0	0	0
Settlements	0	0	0	0
Transfers into Level 3	2	0	2	1
Transfers out of Level 3	(175)	0	(44)	(3)
Balance, end of period	403	231	403	231
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	0	1	0	1
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	0	1	0	1
Separate Accounts
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	959	1,485	1,141	1,558
Total realized/unrealized gains (losses) included in net income (loss)	7	(26)	(22)	7
Total realized/unrealized gains (losses) included in AOCI	0	0	0	0
Purchases	136	4	271	107
Sales	(18)	(24)	(78)	(102)
Issuances	1	30	1	28
Settlements	(1)	(45)	(62)	(57)
Transfers into Level 3	56	8	21	9
Transfers out of Level 3	(101)	(178)	(233)	(296)
Balance, end of period	1,039	1,254	1,039	1,254
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	0	0	0	0
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	$ 0	$ 0	$ 0	$ 0