Fair Value (Unobservable Input Reconciliation) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Residential mortgage loans - FVO
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at January 1,	$ 566	$ 314
Total realized/unrealized gains (losses) included in net income (loss)	40	8	$ 20
Total realized/unrealized gains (losses) included in AOCI	0	0	0
Purchases	175	297
Sales	(179)	(11)
Issuances	0	0
Settlements	(82)	(42)
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Balance at December 31,	520	566	314
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	27	8	20
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	27	8	20
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	53	(56)	(170)
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance at January 1,	(562)	(179)
Total realized/unrealized gains (losses) included in net income (loss)	87	(31)	(149)
Total realized/unrealized gains (losses) included in AOCI	216	(367)	(2)
Purchases	0	28
Sales	0	0
Issuances	(7)	0
Settlements	134	(13)
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Balance at December 31,	(132)	(562)	(179)
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	53	(56)	(170)
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	793	(242)	216
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance at January 1,	(729)	(178)
Total realized/unrealized gains (losses) included in net income (loss)	823	(214)	155
Total realized/unrealized gains (losses) included in AOCI	(46)	(20)	1
Purchases	0	0
Sales	0	0
Issuances	0	0
Settlements	(322)	(317)
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Balance at December 31,	(274)	(729)	(178)
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	793	(242)	216
Corporate fixed maturity securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at January 1,	11,537	10,311
Total realized/unrealized gains (losses) included in net income (loss)	3	5	53
Total realized/unrealized gains (losses) included in AOCI	708	59	(637)
Purchases	3,830	2,754
Sales	(1,763)	(996)
Issuances	0	0
Settlements	0	0
Transfers into Level 3	72	969
Transfers out of Level 3	(3,168)	(1,565)
Balance at December 31,	11,219	11,537	10,311
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	1	6	13
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	6	13
Foreign government
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at January 1,	289	829
Total realized/unrealized gains (losses) included in net income (loss)	4	12	13
Total realized/unrealized gains (losses) included in AOCI	0	(42)	(23)
Purchases	30	44
Sales	(53)	(45)
Issuances	0	0
Settlements	0	0
Transfers into Level 3	5	3
Transfers out of Level 3	(66)	(512)
Balance at December 31,	209	289	829
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	4	12	12
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	4	12	12
Structured Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at January 1,	5,215	5,121
Total realized/unrealized gains (losses) included in net income (loss)	94	103	103
Total realized/unrealized gains (losses) included in AOCI	133	56	(77)
Purchases	1,376	2,221
Sales	(1,598)	(1,483)
Issuances	0	0
Settlements	0	0
Transfers into Level 3	70	25
Transfers out of Level 3	(449)	(828)
Balance at December 31,	4,841	5,215	5,121
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	84	103	103
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	84	103	103
State and political subdivision
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at January 1,	10	34
Total realized/unrealized gains (losses) included in net income (loss)	0	1	0
Total realized/unrealized gains (losses) included in AOCI	0	2	1
Purchases	0	0
Sales	0	0
Issuances	0	0
Settlements	0	0
Transfers into Level 3	0	7
Transfers out of Level 3	(10)	(34)
Balance at December 31,	0	10	34
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	0	1	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	1	0
Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at January 1,	468	334
Total realized/unrealized gains (losses) included in net income (loss)	0	(24)	11
Total realized/unrealized gains (losses) included in AOCI	19	19	(54)
Purchases	25	23
Sales	(51)	(15)
Issuances	0	0
Settlements	0	0
Transfers into Level 3	1	327
Transfers out of Level 3	(34)	(196)
Balance at December 31,	428	468	334
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	(17)	(29)	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	(17)	(29)	0
FVO And Trading Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at January 1,	287	270
Total realized/unrealized gains (losses) included in net income (loss)	22	2	(30)
Total realized/unrealized gains (losses) included in AOCI	0	0	0
Purchases	292	99
Sales	(141)	(35)
Issuances	0	0
Settlements	0	0
Transfers into Level 3	8	18
Transfers out of Level 3	(106)	(67)
Balance at December 31,	362	287	270
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	19	3	(27)
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	19	3	(27)
Short-term Investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at January 1,	46	244
Total realized/unrealized gains (losses) included in net income (loss)	0	1	1
Total realized/unrealized gains (losses) included in AOCI	0	4	(1)
Purchases	32	50
Sales	(1)	(50)
Issuances	0	0
Settlements	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	(44)	(203)
Balance at December 31,	33	46	244
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	0	1	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	1	0
Separate Accounts
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at January 1,	1,141	1,558
Total realized/unrealized gains (losses) included in net income (loss)	(8)	(2)	14
Total realized/unrealized gains (losses) included in AOCI	0	0	0
Purchases	187	375
Sales	(80)	(512)
Issuances	1	62
Settlements	(93)	(51)
Transfers into Level 3	35	19
Transfers out of Level 3	(224)	(308)
Balance at December 31,	959	1,141	1,558
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	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