Fair Value (Unobservable Input Reconciliation) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Net Derivatives
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance at January 1,	$ (279)	$ (954)
Total realized/unrealized gains (losses) included in net income (loss)	152	92	$ (703)
Total realized/unrealized gains (losses) included in AOCI	9	0	4
Purchases	3	4
Sales	(7)	0
Issuances	0	0
Settlements	0	579
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Balance at December 31,	(122)	(279)	(954)
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	148	(52)	(687)
Net Embedded Derivatives
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance at January 1,	(1,660)	(2,383)
Total realized/unrealized gains (losses) included in net income (loss)	526	1,078	(1,842)
Total realized/unrealized gains (losses) included in AOCI	0	0	0
Purchases	0	0
Sales	0	0
Issuances	0	0
Settlements	(864)	(355)
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Balance at December 31,	(1,998)	(1,660)	(2,383)
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	395	966	(1,952)
U.S. corporate and foreign corporate securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at January 1,	1,997	2,391
Total realized/unrealized gains (losses) included in net income (loss)	1	(3)	(11)
Total realized/unrealized gains (losses) included in AOCI	(33)	131	(25)
Purchases	71	441
Sales	(197)	(223)
Issuances	0	0
Settlements	0	0
Transfers into Level 3	418	178
Transfers out of Level 3	(1,525)	(918)
Balance at December 31,	732	1,997	2,391
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	(2)	1	2
Structured securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at January 1,	1,230	1,711
Total realized/unrealized gains (losses) included in net income (loss)	2	28	30
Total realized/unrealized gains (losses) included in AOCI	(6)	52	20
Purchases	42	107
Sales	(91)	(535)
Issuances	0	0
Settlements	0	0
Transfers into Level 3	8	11
Transfers out of Level 3	(1,012)	(144)
Balance at December 31,	173	1,230	1,711
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	0	23	29
State and political subdivision
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at January 1,	0	17
Total realized/unrealized gains (losses) included in net income (loss)	1	0	0
Total realized/unrealized gains (losses) included in AOCI	(1)	0	0
Purchases	0	0
Sales	(1)	0
Issuances	0	0
Settlements	0	0
Transfers into Level 3	75	0
Transfers out of Level 3	0	(17)
Balance at December 31,	74	0	17
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	1	0	0
Foreign government
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at January 1,	5	0
Total realized/unrealized gains (losses) included in net income (loss)	0	0	0
Total realized/unrealized gains (losses) included in AOCI	0	0	0
Purchases	0	5
Sales	(5)	0
Issuances	0	0
Settlements	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Balance at December 31,	0	5	0
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	0	0	0
Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at January 1,	124	137
Total realized/unrealized gains (losses) included in net income (loss)	0	(3)	0
Total realized/unrealized gains (losses) included in AOCI	0	0	(11)
Purchases	1	3
Sales	(3)	(13)
Issuances	0	0
Settlements	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	(119)	0
Balance at December 31,	3	124	137
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	1	0	0
Short-term investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at January 1,	14	2
Total realized/unrealized gains (losses) included in net income (loss)	0	0	0
Total realized/unrealized gains (losses) included in AOCI	0	0	0
Purchases	0	14
Sales	(14)	(1)
Issuances	0	0
Settlements	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	(1)
Balance at December 31,	0	14	2
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	0	0	0
Separate account assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at January 1,	5	10
Total realized/unrealized gains (losses) included in net income (loss)	0	0	0
Total realized/unrealized gains (losses) included in AOCI	0	0	0
Purchases	1	2
Sales	(1)	(4)
Issuances	0	0
Settlements	(1)	(1)
Transfers into Level 3	0	2
Transfers out of Level 3	(3)	(4)
Balance at December 31,	1	5	10
Changes in unrealized gains (losses) included in net income (loss) for the instruments still held at end of period	$ 0	$ 0	$ 0