Fair Value (Unobservable Input Reconciliation) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Net Derivatives
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance, beginning of period	$ (284)	$ (780)	$ (279)	$ (954)
Total realized/unrealized gains (losses) included in net income (loss)	(4)	4	(12)	100
Total realized/unrealized gains (losses) included in AOCI	0	0	0	0
Purchases	0	0	3	4
Sales	0	0	0	0
Issuances	0	0	0	0
Settlements	0	370	0	444
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Balance, end of period	(288)	(406)	(288)	(406)
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	(4)	4	(12)	98
Net Embedded Derivatives
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance, beginning of period	(1,498)	(2,477)	(2,007)	(2,761)
Total realized/unrealized gains (losses) included in net income (loss)	(15)	561	767	1,029
Total realized/unrealized gains (losses) included in AOCI	0	0	0	0
Purchases	0	0	0	0
Sales	0	0	0	0
Issuances	0	0	0	0
Settlements	(152)	(153)	(425)	(337)
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Balance, end of period	(1,665)	(2,069)	(1,665)	(2,069)
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	(13)	341	739	862
U.S. and foreign corporate
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	1,815	2,295	1,937	2,310
Total realized/unrealized gains (losses) included in net income (loss)	0	1	2	(2)
Total realized/unrealized gains (losses) included in AOCI	(44)	34	(118)	176
Purchases	56	92	164	235
Sales	(50)	(56)	(183)	(230)
Issuances	0	0	0	0
Settlements	0	0	0	0
Transfers into Level 3	20	191	20	180
Transfers out of Level 3	(208)	(19)	(233)	(131)
Balance, end of period	1,589	2,538	1,589	2,538
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	0	1	(1)	1
Structured securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	1,261	1,481	1,222	1,695
Total realized/unrealized gains (losses) included in net income (loss)	10	13	21	22
Total realized/unrealized gains (losses) included in AOCI	(8)	6	(10)	43
Purchases	287	147	339	186
Sales	(114)	(230)	(227)	(460)
Issuances	0	0	0	0
Settlements	0	0	0	0
Transfers into Level 3	3	0	0	0
Transfers out of Level 3	(170)	(14)	(76)	(83)
Balance, end of period	1,269	1,403	1,269	1,403
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	4	10	14	19
State and political subdivision
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	8	0	0	17
Total realized/unrealized gains (losses) included in net income (loss)	2	0	0	0
Total realized/unrealized gains (losses) included in AOCI	(2)	0	0	0
Purchases	0	0	0	0
Sales	(6)	(1)	0	(1)
Issuances	0	0	0	0
Settlements	0	0	0	0
Transfers into Level 3	0	10	0	3
Transfers out of Level 3	(2)	0	0	(10)
Balance, end of period	0	9	0	9
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	0	0	0	0
Foreign government
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	0	0	5	0
Total realized/unrealized gains (losses) included in net income (loss)	0	0	0	0
Total realized/unrealized gains (losses) included in AOCI	0	0	0	0
Purchases	0	0	0	0
Sales	0	0	0	0
Issuances	0	0	0	0
Settlements	0	0	0	0
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	(5)	0
Balance, end of period	0	0	0	0
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	0	0	0	0
Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	120	134	124	137
Total realized/unrealized gains (losses) included in net income (loss)	(2)	0	(4)	0
Total realized/unrealized gains (losses) included in AOCI	0	(1)	0	2
Purchases	0	0	0	4
Sales	0	(3)	(3)	(13)
Issuances	0	0	0	0
Settlements	0	0	0	0
Transfers into Level 3	9	0	10	0
Transfers out of Level 3	(5)	0	(5)	0
Balance, end of period	122	130	122	130
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	0	0	(4)	0
Real estate joint ventures
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	17	0	22	0
Total realized/unrealized gains (losses) included in net income (loss)	0	0	(1)	0
Total realized/unrealized gains (losses) included in AOCI	0	0	0	0
Purchases	0	0	0	0
Sales	(2)	0	(6)	0
Issuances	0	0	0	0
Settlements	0	0	0	0
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Balance, end of period	15	0	15	0
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	0	0	(1)	0
Other limited partnership interests
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	24	0	28	0
Total realized/unrealized gains (losses) included in net income (loss)	3	0	2	0
Total realized/unrealized gains (losses) included in AOCI	(1)	0	(1)	0
Purchases	0	0	0	0
Sales	(1)	0	(4)	0
Issuances	0	0	0	0
Settlements	0	0	0	0
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Balance, end of period	25	0	25	0
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	3	0	2	0
Short-term investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	0	91	14	2
Total realized/unrealized gains (losses) included in net income (loss)	0	0	0	0
Total realized/unrealized gains (losses) included in AOCI	0	0	0	0
Purchases	0	0	0	1
Sales	0	0	(14)	(1)
Issuances	0	0	0	0
Settlements	0	0	0	0
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	(90)	0	(1)
Balance, end of period	0	1	0	1
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	0	0	0	0
Separate account assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	4	6	5	10
Total realized/unrealized gains (losses) included in net income (loss)	0	0	0	0
Total realized/unrealized gains (losses) included in AOCI	0	0	0	0
Purchases	1	2	1	2
Sales	0	0	(1)	(3)
Issuances	0	0	0	0
Settlements	0	0	(1)	0
Transfers into Level 3	0	0	0	1
Transfers out of Level 3	(1)	(2)	0	(4)
Balance, end of period	4	6	4	6
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	$ 0	$ 0	$ 0	$ 0