Fair Value (Unobservable Input Reconciliation) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Residential mortgage loans - FVO
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	$ 520	$ 566
Total realized/unrealized gains (losses) included in net income (loss)	2	(3)
Total realized/unrealized gains (losses) included in AOCI	0	0
Purchases	0	135
Sales	(64)	(33)
Issuances	0	0
Settlements	(20)	(26)
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Balance, end of period	438	639
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	(8)	(3)
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	(8)	(3)
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	48	26
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance, beginning of period	(132)	(562)
Total realized/unrealized gains (losses) included in net income (loss)	11	33
Total realized/unrealized gains (losses) included in AOCI	(104)	44
Purchases	0	0
Sales	0	0
Issuances	0	(7)
Settlements	43	95
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Balance, end of period	(182)	(397)
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	48	26
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	31	167
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance, beginning of period	(274)	(729)
Total realized/unrealized gains (losses) included in net income (loss)	36	169
Total realized/unrealized gains (losses) included in AOCI	(16)	(59)
Purchases	0	0
Sales	0	0
Issuances	0	0
Settlements	(74)	(76)
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Balance, end of period	(328)	(695)
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	31	167
Corporate fixed maturity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	11,219	11,537
Total realized/unrealized gains (losses) included in net income (loss)	7	4
Total realized/unrealized gains (losses) included in AOCI	(68)	231
Purchases	512	941
Sales	(542)	(418)
Issuances	0	0
Settlements	0	0
Transfers into Level 3	46	79
Transfers out of Level 3	(364)	(1,406)
Balance, end of period	10,810	10,968
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	1	4
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	4
Foreign government
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	209	289
Total realized/unrealized gains (losses) included in net income (loss)	1	3
Total realized/unrealized gains (losses) included in AOCI	(3)	6
Purchases	2	12
Sales	(2)	(17)
Issuances	0	0
Settlements	0	0
Transfers into Level 3	0	4
Transfers out of Level 3	(28)	(8)
Balance, end of period	179	289
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	1	2
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
Structured Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	4,841	5,215
Total realized/unrealized gains (losses) included in net income (loss)	23	32
Total realized/unrealized gains (losses) included in AOCI	24	48
Purchases	657	1,020
Sales	(324)	(400)
Issuances	0	0
Settlements	0	0
Transfers into Level 3	45	23
Transfers out of Level 3	(684)	(233)
Balance, end of period	4,582	5,705
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	21	24
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	21	24
State and political subdivision
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	0	10
Total realized/unrealized gains (losses) included in net income (loss)	0	0
Total realized/unrealized gains (losses) included in AOCI	0	0
Purchases	0	0
Sales	0	0
Issuances	0	0
Settlements	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	(10)
Balance, end of period	0	0
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	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
Equity Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	428	468
Total realized/unrealized gains (losses) included in net income (loss)	(6)	(10)
Total realized/unrealized gains (losses) included in AOCI	0	22
Purchases	1	1
Sales	(1)	(1)
Issuances	0	0
Settlements	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Balance, end of period	422	480
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	0	(10)
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	(10)
FVO Securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	362	287
Total realized/unrealized gains (losses) included in net income (loss)	5	7
Total realized/unrealized gains (losses) included in AOCI	0	0
Purchases	27	69
Sales	(59)	(17)
Issuances	0	0
Settlements	0	0
Transfers into Level 3	0	2
Transfers out of Level 3	(49)	(13)
Balance, end of period	286	335
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	4	7
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	7
Other limited partnership interests
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	0	0
Total realized/unrealized gains (losses) included in net income (loss)	(5)	0
Total realized/unrealized gains (losses) included in AOCI	2	0
Purchases	0	0
Sales	(19)	0
Issuances	0	0
Settlements	0	0
Transfers into Level 3	216	0
Transfers out of Level 3	0	0
Balance, end of period	194	0
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	(5)	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	(5)	0
Short-term Investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	33	46
Total realized/unrealized gains (losses) included in net income (loss)	0	0
Total realized/unrealized gains (losses) included in AOCI	0	0
Purchases	605	776
Sales	(3)	(3)
Issuances	0	0
Settlements	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	(20)	(40)
Balance, end of period	615	779
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	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
Separate Accounts
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	959	1,141
Total realized/unrealized gains (losses) included in net income (loss)	2	(24)
Total realized/unrealized gains (losses) included in AOCI	0	0
Purchases	409	136
Sales	(124)	(42)
Issuances	1	39
Settlements	(1)	(33)
Transfers into Level 3	53	69
Transfers out of Level 3	(75)	(102)
Balance, end of period	1,224	1,184
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	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