Fair Value (Recurring Fair Value Measurements) (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Assets [Abstract]
Debt Securities, Available-for-sale	$ 304,840	$ 308,931
Available-for-sale Securities, Equity Securities	1,479	2,513
Debt Securities, Trading, and Equity Securities, FV-NI	13,540	16,745
Short-term investments	5,231	4,870
Mortgage loans, at estimated fair value, relating to variable interest entities	72,461	68,731
Derivative assets	7,288	8,551
Embedded derivatives within asset host contracts	57	12
Separate account assets	185,416	205,001
Liabilities [Abstract]
Derivative liabilities	4,517	4,339
Embedded derivatives within liability host contracts	196	418
Separate account liabilities	185,416	205,001
Net Embedded Derivatives
Assets [Abstract]
Debt and equity securities also included in embedded derivatives	0	(132)
Residential mortgage loans - FVO
Assets [Abstract]
Mortgage loans, at estimated fair value, relating to variable interest entities	323	520
Recurring
Assets [Abstract]
Debt Securities, Available-for-sale	304,840	308,931
Available-for-sale Securities, Equity Securities	1,479	2,513
Debt Securities, Trading, and Equity Securities, FV-NI	13,540	16,745
Other limited partnership interests	155
Short-term investments	4,568	4,286
Other investments	196	165
Derivative assets	7,288	8,551
Embedded derivatives within asset host contracts	57	144
Separate account assets	185,416	205,001
Total assets	517,862	546,856
Liabilities [Abstract]
Derivative liabilities	4,517	4,339
Embedded derivatives within liability host contracts	196	418
Total liabilities	4,729	4,766
Recurring | Interest rate contracts
Assets [Abstract]
Derivative assets	4,047	5,563
Liabilities [Abstract]
Derivative liabilities	647	772
Recurring | Foreign currency exchange rate contracts
Assets [Abstract]
Derivative assets	2,312	2,069
Liabilities [Abstract]
Derivative liabilities	2,860	2,590
Recurring | Credit contracts
Assets [Abstract]
Derivative assets	249	278
Liabilities [Abstract]
Derivative liabilities	43	43
Recurring | Equity market contracts
Assets [Abstract]
Derivative assets	680	641
Liabilities [Abstract]
Derivative liabilities	967	934
Recurring | Derivative Liabilities Within Separate Accounts
Liabilities [Abstract]
Separate account liabilities	16	9
Recurring | Residential mortgage loans - FVO
Assets [Abstract]
Mortgage loans, at estimated fair value, relating to variable interest entities	323	520
Recurring | U.S. corporate
Assets [Abstract]
Debt Securities, Available-for-sale	83,795	82,661
Recurring | Foreign government
Assets [Abstract]
Debt Securities, Available-for-sale	60,472	61,534
Recurring | Foreign corporate
Assets [Abstract]
Debt Securities, Available-for-sale	54,220	55,569
Recurring | U.S. government and agency
Assets [Abstract]
Debt Securities, Available-for-sale	45,572	47,394
Recurring | RMBS
Assets [Abstract]
Debt Securities, Available-for-sale	27,658	28,800
Recurring | State and political subdivision
Assets [Abstract]
Debt Securities, Available-for-sale	11,600	12,455
Recurring | ABS
Assets [Abstract]
Debt Securities, Available-for-sale	12,815	12,291
Recurring | CMBS
Assets [Abstract]
Debt Securities, Available-for-sale	8,708	8,227
Recurring | Level 1
Assets [Abstract]
Debt Securities, Available-for-sale	25,246	26,052
Available-for-sale Securities, Equity Securities	941	1,104
Debt Securities, Trading, and Equity Securities, FV-NI	11,235	14,028
Other limited partnership interests	0
Short-term investments	1,615	3,001
Other investments	85	81
Derivative assets	9	22
Embedded derivatives within asset host contracts	0	0
Separate account assets	83,754	89,916
Total assets	122,885	134,204
Liabilities [Abstract]
Derivative liabilities	14	8
Embedded derivatives within liability host contracts	0	0
Total liabilities	14	8
Recurring | Level 1 | Interest rate contracts
Assets [Abstract]
Derivative assets	1	2
Liabilities [Abstract]
Derivative liabilities	4	4
Recurring | Level 1 | Foreign currency exchange rate contracts
Assets [Abstract]
Derivative assets	0	2
Liabilities [Abstract]
Derivative liabilities	5	0
Recurring | Level 1 | Credit contracts
Assets [Abstract]
Derivative assets	0	0
Liabilities [Abstract]
Derivative liabilities	0	0
Recurring | Level 1 | Equity market contracts
Assets [Abstract]
Derivative assets	8	18
Liabilities [Abstract]
Derivative liabilities	5	4
Recurring | Level 1 | Derivative Liabilities Within Separate Accounts
Liabilities [Abstract]
Separate account liabilities	0	0
Recurring | Level 1 | Residential mortgage loans - FVO
Assets [Abstract]
Mortgage loans, at estimated fair value, relating to variable interest entities	0	0
Recurring | Level 1 | U.S. corporate
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 1 | Foreign 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	25,246	26,052
Recurring | Level 1 | RMBS
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 | CMBS
Assets [Abstract]
Debt Securities, Available-for-sale	0	0
Recurring | Level 2
Assets [Abstract]
Debt Securities, Available-for-sale	264,905	266,610
Available-for-sale Securities, Equity Securities	95	981
Debt Securities, Trading, and Equity Securities, FV-NI	2,079	2,355
Other limited partnership interests	0
Short-term investments	2,299	1,252
Other investments	111	84
Derivative assets	7,097	8,295
Embedded derivatives within asset host contracts	0	0
Separate account assets	100,653	114,124
Total assets	377,239	393,701
Liabilities [Abstract]
Derivative liabilities	3,914	3,965
Embedded derivatives within liability host contracts	0	0
Total liabilities	3,922	3,972
Recurring | Level 2 | Interest rate contracts
Assets [Abstract]
Derivative assets	4,046	5,553
Liabilities [Abstract]
Derivative liabilities	316	638
Recurring | Level 2 | Foreign currency exchange rate contracts
Assets [Abstract]
Derivative assets	2,234	1,954
Liabilities [Abstract]
Derivative liabilities	2,799	2,553
Recurring | Level 2 | Credit contracts
Assets [Abstract]
Derivative assets	214	240
Liabilities [Abstract]
Derivative liabilities	43	43
Recurring | Level 2 | Equity market contracts
Assets [Abstract]
Derivative assets	603	548
Liabilities [Abstract]
Derivative liabilities	756	731
Recurring | Level 2 | Derivative Liabilities Within Separate Accounts
Liabilities [Abstract]
Separate account liabilities	8	7
Recurring | Level 2 | Residential mortgage loans - FVO
Assets [Abstract]
Mortgage loans, at estimated fair value, relating to variable interest entities	0	0
Recurring | Level 2 | U.S. corporate
Assets [Abstract]
Debt Securities, Available-for-sale	79,812	78,171
Recurring | Level 2 | Foreign government
Assets [Abstract]
Debt Securities, Available-for-sale	60,332	61,325
Recurring | Level 2 | Foreign corporate
Assets [Abstract]
Debt Securities, Available-for-sale	47,870	48,840
Recurring | Level 2 | U.S. government and agency
Assets [Abstract]
Debt Securities, Available-for-sale	20,326	21,342
Recurring | Level 2 | RMBS
Assets [Abstract]
Debt Securities, Available-for-sale	24,560	25,339
Recurring | Level 2 | State and political subdivision
Assets [Abstract]
Debt Securities, Available-for-sale	11,600	12,455
Recurring | Level 2 | ABS
Assets [Abstract]
Debt Securities, Available-for-sale	12,030	11,204
Recurring | Level 2 | CMBS
Assets [Abstract]
Debt Securities, Available-for-sale	8,375	7,934
Recurring | Level 3
Assets [Abstract]
Debt Securities, Available-for-sale	14,689	16,269
Available-for-sale Securities, Equity Securities	443	428
Debt Securities, Trading, and Equity Securities, FV-NI	226	362
Other limited partnership interests	155
Short-term investments	654	33
Other investments	0	0
Derivative assets	182	234
Embedded derivatives within asset host contracts	57	144
Separate account assets	1,009	961
Total assets	17,738	18,951
Liabilities [Abstract]
Derivative liabilities	589	366
Embedded derivatives within liability host contracts	196	418
Total liabilities	793	786
Recurring | Level 3 | Interest rate contracts
Assets [Abstract]
Derivative assets	0	8
Liabilities [Abstract]
Derivative liabilities	327	130
Recurring | Level 3 | Foreign currency exchange rate contracts
Assets [Abstract]
Derivative assets	78	113
Liabilities [Abstract]
Derivative liabilities	56	37
Recurring | Level 3 | Credit contracts
Assets [Abstract]
Derivative assets	35	38
Liabilities [Abstract]
Derivative liabilities	0	0
Recurring | Level 3 | Equity market contracts
Assets [Abstract]
Derivative assets	69	75
Liabilities [Abstract]
Derivative liabilities	206	199
Recurring | Level 3 | Derivative Liabilities Within Separate Accounts
Liabilities [Abstract]
Separate account liabilities	8	2
Recurring | Level 3 | Residential mortgage loans - FVO
Assets [Abstract]
Mortgage loans, at estimated fair value, relating to variable interest entities	323	520
Recurring | Level 3 | U.S. corporate
Assets [Abstract]
Debt Securities, Available-for-sale	3,983	4,490
Recurring | Level 3 | Foreign government
Assets [Abstract]
Debt Securities, Available-for-sale	140	209
Recurring | Level 3 | Foreign corporate
Assets [Abstract]
Debt Securities, Available-for-sale	6,350	6,729
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	3,098	3,461
Recurring | Level 3 | State and political subdivision
Assets [Abstract]
Debt Securities, Available-for-sale	0	0
Recurring | Level 3 | ABS
Assets [Abstract]
Debt Securities, Available-for-sale	785	1,087
Recurring | Level 3 | CMBS
Assets [Abstract]
Debt Securities, Available-for-sale	$ 333	$ 293