Fair Value (Recurring Fair Value Measurements) (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Assets [Abstract]
Debt Securities, Available-for-sale	$ 306,331	$ 308,931
Available-for-sale Securities, Equity Securities	1,483	2,513
Debt Securities, Trading, and Equity Securities, FV-NI	13,848	16,745
Short-term investments	3,853	4,870
Mortgage Loans on Real Estate, Commercial and Consumer, Net	70,852	68,731
Derivative assets	7,868	8,551
Embedded derivatives within asset host contracts	153	12
Separate account assets	191,347	205,001
Liabilities [Abstract]
Derivative liabilities	4,135	4,339
Embedded derivatives within liability host contracts	393	418
Separate account liabilities	$ 191,347	$ 205,001
Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Percentage of Unit-linked investments within Unit-linked and FVO Securities	85.00%	85.00%
Net Embedded Derivatives
Assets [Abstract]
Debt and equity securities also included in embedded derivatives	$ 0	$ (132)
Residential mortgage loans - FVO
Assets [Abstract]
Mortgage Loans on Real Estate, Commercial and Consumer, Net	405	520
Recurring
Assets [Abstract]
Debt Securities, Available-for-sale	306,331	308,931
Available-for-sale Securities, Equity Securities	1,483	2,513
Debt Securities, Trading, and Equity Securities, FV-NI	13,848	16,745
Other limited partnership interests	168
Short-term investments	3,175	4,286
Other investments	185	165
Derivative assets	7,868	8,551
Embedded derivatives within asset host contracts	153	144
Separate account assets	191,347	205,001
Total assets	524,963	546,856
Liabilities [Abstract]
Derivative liabilities	4,135	4,339
Embedded derivatives within liability host contracts	393	418
Total liabilities	4,546	4,766
Recurring | Interest rate contracts
Assets [Abstract]
Derivative assets	4,575	5,563
Liabilities [Abstract]
Derivative liabilities	521	772
Recurring | Foreign currency exchange rate contracts
Assets [Abstract]
Derivative assets	2,373	2,069
Liabilities [Abstract]
Derivative liabilities	2,681	2,590
Recurring | Credit contracts
Assets [Abstract]
Derivative assets	213	278
Liabilities [Abstract]
Derivative liabilities	44	43
Recurring | Equity market contracts
Assets [Abstract]
Derivative assets	707	641
Liabilities [Abstract]
Derivative liabilities	889	934
Recurring | Derivative Liabilities Within Separate Accounts
Liabilities [Abstract]
Separate account liabilities	18	9
Recurring | Residential mortgage loans - FVO
Assets [Abstract]
Mortgage Loans on Real Estate, Commercial and Consumer, Net	405	520
Recurring | U.S. corporate
Assets [Abstract]
Debt Securities, Available-for-sale	84,026	82,661
Recurring | Foreign government
Assets [Abstract]
Debt Securities, Available-for-sale	61,682	61,534
Recurring | Foreign corporate
Assets [Abstract]
Debt Securities, Available-for-sale	54,277	55,569
Recurring | U.S. government and agency
Assets [Abstract]
Debt Securities, Available-for-sale	45,387	47,394
Recurring | RMBS
Assets [Abstract]
Debt Securities, Available-for-sale	27,845	28,800
Recurring | State and political subdivision
Assets [Abstract]
Debt Securities, Available-for-sale	12,026	12,455
Recurring | ABS
Assets [Abstract]
Debt Securities, Available-for-sale	12,866	12,291
Recurring | CMBS
Assets [Abstract]
Debt Securities, Available-for-sale	8,222	8,227
Recurring | Level 1
Assets [Abstract]
Debt Securities, Available-for-sale	24,231	26,052
Available-for-sale Securities, Equity Securities	936	1,104
Debt Securities, Trading, and Equity Securities, FV-NI	11,526	14,028
Other limited partnership interests	0
Short-term investments	936	3,001
Other investments	85	81
Derivative assets	4	22
Embedded derivatives within asset host contracts	0	0
Separate account assets	84,346	89,916
Total assets	122,064	134,204
Liabilities [Abstract]
Derivative liabilities	15	8
Embedded derivatives within liability host contracts	0	0
Total liabilities	19	8
Recurring | Level 1 | Interest rate contracts
Assets [Abstract]
Derivative assets	1	2
Liabilities [Abstract]
Derivative liabilities	5	4
Recurring | Level 1 | Foreign currency exchange rate contracts
Assets [Abstract]
Derivative assets	0	2
Liabilities [Abstract]
Derivative liabilities	6	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	3	18
Liabilities [Abstract]
Derivative liabilities	4	4
Recurring | Level 1 | Derivative Liabilities Within Separate Accounts
Liabilities [Abstract]
Separate account liabilities	4	0
Recurring | Level 1 | Residential mortgage loans - FVO
Assets [Abstract]
Mortgage Loans on Real Estate, Commercial and Consumer, Net	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	24,231	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	266,638	266,610
Available-for-sale Securities, Equity Securities	139	981
Debt Securities, Trading, and Equity Securities, FV-NI	2,053	2,355
Other limited partnership interests	0
Short-term investments	1,680	1,252
Other investments	100	84
Derivative assets	7,659	8,295
Embedded derivatives within asset host contracts	0	0
Separate account assets	105,856	114,124
Total assets	384,125	393,701
Liabilities [Abstract]
Derivative liabilities	3,648	3,965
Embedded derivatives within liability host contracts	0	0
Total liabilities	3,655	3,972
Recurring | Level 2 | Interest rate contracts
Assets [Abstract]
Derivative assets	4,548	5,553
Liabilities [Abstract]
Derivative liabilities	295	638
Recurring | Level 2 | Foreign currency exchange rate contracts
Assets [Abstract]
Derivative assets	2,296	1,954
Liabilities [Abstract]
Derivative liabilities	2,624	2,553
Recurring | Level 2 | Credit contracts
Assets [Abstract]
Derivative assets	179	240
Liabilities [Abstract]
Derivative liabilities	44	43
Recurring | Level 2 | Equity market contracts
Assets [Abstract]
Derivative assets	636	548
Liabilities [Abstract]
Derivative liabilities	685	731
Recurring | Level 2 | Derivative Liabilities Within Separate Accounts
Liabilities [Abstract]
Separate account liabilities	7	7
Recurring | Level 2 | Residential mortgage loans - FVO
Assets [Abstract]
Mortgage Loans on Real Estate, Commercial and Consumer, Net	0	0
Recurring | Level 2 | U.S. corporate
Assets [Abstract]
Debt Securities, Available-for-sale	79,872	78,171
Recurring | Level 2 | Foreign government
Assets [Abstract]
Debt Securities, Available-for-sale	61,526	61,325
Recurring | Level 2 | Foreign corporate
Assets [Abstract]
Debt Securities, Available-for-sale	47,810	48,840
Recurring | Level 2 | U.S. government and agency
Assets [Abstract]
Debt Securities, Available-for-sale	21,156	21,342
Recurring | Level 2 | RMBS
Assets [Abstract]
Debt Securities, Available-for-sale	24,774	25,339
Recurring | Level 2 | State and political subdivision
Assets [Abstract]
Debt Securities, Available-for-sale	12,018	12,455
Recurring | Level 2 | ABS
Assets [Abstract]
Debt Securities, Available-for-sale	11,649	11,204
Recurring | Level 2 | CMBS
Assets [Abstract]
Debt Securities, Available-for-sale	7,833	7,934
Recurring | Level 3
Assets [Abstract]
Debt Securities, Available-for-sale	15,462	16,269
Available-for-sale Securities, Equity Securities	408	428
Debt Securities, Trading, and Equity Securities, FV-NI	269	362
Other limited partnership interests	168
Short-term investments	559	33
Other investments	0	0
Derivative assets	205	234
Embedded derivatives within asset host contracts	153	144
Separate account assets	1,145	961
Total assets	18,774	18,951
Liabilities [Abstract]
Derivative liabilities	472	366
Embedded derivatives within liability host contracts	393	418
Total liabilities	872	786
Recurring | Level 3 | Interest rate contracts
Assets [Abstract]
Derivative assets	26	8
Liabilities [Abstract]
Derivative liabilities	221	130
Recurring | Level 3 | Foreign currency exchange rate contracts
Assets [Abstract]
Derivative assets	77	113
Liabilities [Abstract]
Derivative liabilities	51	37
Recurring | Level 3 | Credit contracts
Assets [Abstract]
Derivative assets	34	38
Liabilities [Abstract]
Derivative liabilities	0	0
Recurring | Level 3 | Equity market contracts
Assets [Abstract]
Derivative assets	68	75
Liabilities [Abstract]
Derivative liabilities	200	199
Recurring | Level 3 | Derivative Liabilities Within Separate Accounts
Liabilities [Abstract]
Separate account liabilities	7	2
Recurring | Level 3 | Residential mortgage loans - FVO
Assets [Abstract]
Mortgage Loans on Real Estate, Commercial and Consumer, Net	405	520
Recurring | Level 3 | U.S. corporate
Assets [Abstract]
Debt Securities, Available-for-sale	4,154	4,490
Recurring | Level 3 | Foreign government
Assets [Abstract]
Debt Securities, Available-for-sale	156	209
Recurring | Level 3 | Foreign corporate
Assets [Abstract]
Debt Securities, Available-for-sale	6,467	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	3,071	3,461
Recurring | Level 3 | State and political subdivision
Assets [Abstract]
Debt Securities, Available-for-sale	8	0
Recurring | Level 3 | ABS
Assets [Abstract]
Debt Securities, Available-for-sale	1,217	1,087
Recurring | Level 3 | CMBS
Assets [Abstract]
Debt Securities, Available-for-sale	$ 389	$ 293