Fair Value (Recurring Fair Value Measurements) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Assets [Abstract]
Debt Securities, Available-for-sale	$ 63,590	$ 61,348
Equity securities	150	140
Short-term Investments	506	0
Derivative assets: (1)	2,059	2,765
Separate account assets	97,924	91,511
Liabilities [Abstract]
Derivative liabilities: (1)	2,586	2,112
Embedded derivatives within liability host contracts	2,946	2,516
Recurring
Assets [Abstract]
Debt Securities, Available-for-sale	63,590	61,348
Equity securities	150	140
Short-term Investments	506
Derivative assets: (1)	2,059	2,765
Embedded derivatives within asset host contracts	219	228
Separate account assets	97,924	91,511
Total assets	164,448	155,992
Liabilities [Abstract]
Derivative liabilities: (1)	2,586	2,112
Embedded derivatives within liability host contracts	2,946	2,516
Total liabilities	5,532	4,628
Recurring | Interest rate derivatives
Assets [Abstract]
Derivative assets: (1)	916	717
Liabilities [Abstract]
Derivative liabilities: (1)	530	619
Recurring | Foreign currency exchange rate
Assets [Abstract]
Derivative assets: (1)	256	299
Liabilities [Abstract]
Derivative liabilities: (1)	55	48
Recurring | Credit
Assets [Abstract]
Derivative assets: (1)	25	17
Liabilities [Abstract]
Derivative liabilities: (1)	0	3
Recurring | Equity market
Assets [Abstract]
Derivative assets: (1)	862	1,732
Liabilities [Abstract]
Derivative liabilities: (1)	2,001	1,442
Recurring | U.S. corporate
Assets [Abstract]
Debt Securities, Available-for-sale	25,448	24,059
Recurring | U.S. government and agency
Assets [Abstract]
Debt Securities, Available-for-sale	7,686	8,644
Recurring | RMBS
Assets [Abstract]
Debt Securities, Available-for-sale	8,760	8,435
Recurring | Foreign corporate
Assets [Abstract]
Debt Securities, Available-for-sale	8,904	7,895
Recurring | CMBS
Assets [Abstract]
Debt Securities, Available-for-sale	5,304	5,133
Recurring | State and political subdivision
Assets [Abstract]
Debt Securities, Available-for-sale	3,794	3,586
Recurring | ABS
Assets [Abstract]
Debt Securities, Available-for-sale	2,063	2,111
Recurring | Foreign government
Assets [Abstract]
Debt Securities, Available-for-sale	1,631	1,485
Recurring | Level 1
Assets [Abstract]
Debt Securities, Available-for-sale	1,741	2,334
Equity securities	14	13
Short-term Investments	339
Derivative assets: (1)	0	0
Embedded derivatives within asset host contracts	0	0
Separate account assets	262	217
Total assets	2,356	2,564
Liabilities [Abstract]
Derivative liabilities: (1)	0	0
Embedded derivatives within liability host contracts	0	0
Total liabilities	0	0
Recurring | Level 1 | Interest rate derivatives
Assets [Abstract]
Derivative assets: (1)	0	0
Liabilities [Abstract]
Derivative liabilities: (1)	0	0
Recurring | Level 1 | Foreign currency exchange rate
Assets [Abstract]
Derivative assets: (1)	0	0
Liabilities [Abstract]
Derivative liabilities: (1)	0	0
Recurring | Level 1 | Credit
Assets [Abstract]
Derivative assets: (1)	0	0
Liabilities [Abstract]
Derivative liabilities: (1)	0	0
Recurring | Level 1 | Equity market
Assets [Abstract]
Derivative assets: (1)	0	0
Liabilities [Abstract]
Derivative liabilities: (1)	0	0
Recurring | Level 1 | U.S. corporate
Assets [Abstract]
Debt Securities, Available-for-sale	0	0
Recurring | Level 1 | U.S. government and agency
Assets [Abstract]
Debt Securities, Available-for-sale	1,741	2,334
Recurring | Level 1 | RMBS
Assets [Abstract]
Debt Securities, Available-for-sale	0	0
Recurring | Level 1 | Foreign corporate
Assets [Abstract]
Debt Securities, Available-for-sale	0	0
Recurring | Level 1 | CMBS
Assets [Abstract]
Debt Securities, Available-for-sale	0	0
Recurring | Level 1 | State and political subdivision
Assets [Abstract]
Debt Securities, Available-for-sale	0	0
Recurring | Level 1 | ABS
Assets [Abstract]
Debt Securities, Available-for-sale	0	0
Recurring | Level 1 | Foreign government
Assets [Abstract]
Debt Securities, Available-for-sale	0	0
Recurring | Level 2
Assets [Abstract]
Debt Securities, Available-for-sale	60,868	58,055
Equity securities	132	124
Short-term Investments	167
Derivative assets: (1)	1,946	2,649
Embedded derivatives within asset host contracts	0	0
Separate account assets	97,662	91,293
Total assets	160,775	152,121
Liabilities [Abstract]
Derivative liabilities: (1)	2,337	1,874
Embedded derivatives within liability host contracts	0	0
Total liabilities	2,337	1,874
Recurring | Level 2 | Interest rate derivatives
Assets [Abstract]
Derivative assets: (1)	916	717
Liabilities [Abstract]
Derivative liabilities: (1)	530	619
Recurring | Level 2 | Foreign currency exchange rate
Assets [Abstract]
Derivative assets: (1)	250	288
Liabilities [Abstract]
Derivative liabilities: (1)	53	48
Recurring | Level 2 | Credit
Assets [Abstract]
Derivative assets: (1)	18	10
Liabilities [Abstract]
Derivative liabilities: (1)	0	2
Recurring | Level 2 | Equity market
Assets [Abstract]
Derivative assets: (1)	762	1,634
Liabilities [Abstract]
Derivative liabilities: (1)	1,754	1,205
Recurring | Level 2 | U.S. corporate
Assets [Abstract]
Debt Securities, Available-for-sale	25,158	23,740
Recurring | Level 2 | U.S. government and agency
Assets [Abstract]
Debt Securities, Available-for-sale	5,945	6,310
Recurring | Level 2 | RMBS
Assets [Abstract]
Debt Securities, Available-for-sale	8,741	8,429
Recurring | Level 2 | Foreign corporate
Assets [Abstract]
Debt Securities, Available-for-sale	8,515	7,503
Recurring | Level 2 | CMBS
Assets [Abstract]
Debt Securities, Available-for-sale	5,176	5,004
Recurring | Level 2 | State and political subdivision
Assets [Abstract]
Debt Securities, Available-for-sale	3,720	3,512
Recurring | Level 2 | ABS
Assets [Abstract]
Debt Securities, Available-for-sale	1,982	2,072
Recurring | Level 2 | Foreign government
Assets [Abstract]
Debt Securities, Available-for-sale	1,631	1,485
Recurring | Level 3
Assets [Abstract]
Debt Securities, Available-for-sale	981	959
Equity securities	4	3
Short-term Investments	0
Derivative assets: (1)	113	116
Embedded derivatives within asset host contracts	219	228
Separate account assets	0	1
Total assets	1,317	1,307
Liabilities [Abstract]
Derivative liabilities: (1)	249	238
Embedded derivatives within liability host contracts	2,946	2,516
Total liabilities	3,195	2,754
Recurring | Level 3 | Interest rate derivatives
Assets [Abstract]
Derivative assets: (1)	0	0
Liabilities [Abstract]
Derivative liabilities: (1)	0	0
Recurring | Level 3 | Foreign currency exchange rate
Assets [Abstract]
Derivative assets: (1)	6	11
Liabilities [Abstract]
Derivative liabilities: (1)	2	0
Recurring | Level 3 | Credit
Assets [Abstract]
Derivative assets: (1)	7	7
Liabilities [Abstract]
Derivative liabilities: (1)	0	1
Recurring | Level 3 | Equity market
Assets [Abstract]
Derivative assets: (1)	100	98
Liabilities [Abstract]
Derivative liabilities: (1)	247	237
Recurring | Level 3 | U.S. corporate
Assets [Abstract]
Debt Securities, Available-for-sale	290	319
Recurring | Level 3 | U.S. government and agency
Assets [Abstract]
Debt Securities, Available-for-sale	0	0
Recurring | Level 3 | RMBS
Assets [Abstract]
Debt Securities, Available-for-sale	19	6
Recurring | Level 3 | Foreign corporate
Assets [Abstract]
Debt Securities, Available-for-sale	389	392
Recurring | Level 3 | CMBS
Assets [Abstract]
Debt Securities, Available-for-sale	128	129
Recurring | Level 3 | State and political subdivision
Assets [Abstract]
Debt Securities, Available-for-sale	74	74
Recurring | Level 3 | ABS
Assets [Abstract]
Debt Securities, Available-for-sale	81	39
Recurring | Level 3 | Foreign government
Assets [Abstract]
Debt Securities, Available-for-sale	$ 0	$ 0