Fair Value (Recurring Fair Value Measurements) (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Assets [Abstract]
Debt Securities, Available-for-sale	$ 60,627	$ 63,333
Available-for-sale Securities, Equity Securities	150	161
Short-term Investments	116	269
Mortgage Loans on Real Estate, Commerical and Consumer Net	12,934	10,640
Derivative assets	1,846	2,244
Embedded derivatives within asset host contracts	166	175
Separate account assets	103,898	110,156
Liabilities [Abstract]
Derivative liabilities	3,304	3,129
Embedded derivatives within liability host contracts	1,831	2,234
Long-term debt, at estimated fair value, relating to variable interest entities	237	46
Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	0	(52)
Assets [Abstract]
Debt Securities, Available-for-sale	60,627	63,333
Available-for-sale Securities, Equity Securities	150	161
Short-term Investments	116	269
Real Estate Investments, Joint Ventures	15
Other limited partnership interests	25
Derivative assets	1,846	2,244
Embedded derivatives within asset host contracts	166	227
Separate account assets	103,898	110,156
Total assets	166,936	176,505
Liabilities [Abstract]
Derivative liabilities	3,304	3,129
Embedded derivatives within liability host contracts	1,831	2,234
Total liabilities	5,138	5,374
Recurring | Interest rate contracts
Assets [Abstract]
Derivative assets	629	1,112
Liabilities [Abstract]
Derivative liabilities	1,044	837
Recurring | Foreign currency exchange rate contracts
Assets [Abstract]
Derivative assets	176	155
Liabilities [Abstract]
Derivative liabilities	93	118
Recurring | Credit contracts
Assets [Abstract]
Derivative assets	34	40
Liabilities [Abstract]
Derivative liabilities	1	1
Recurring | Equity market contracts
Assets [Abstract]
Derivative assets	1,007	937
Liabilities [Abstract]
Derivative liabilities	2,166	2,173
Recurring | U.S. corporate
Assets [Abstract]
Debt Securities, Available-for-sale	23,404	22,380
Recurring | U.S. government and agency
Assets [Abstract]
Debt Securities, Available-for-sale	10,505	15,913
Recurring | RMBS
Assets [Abstract]
Debt Securities, Available-for-sale	8,207	7,817
Recurring | Foreign corporate
Assets [Abstract]
Debt Securities, Available-for-sale	7,045	6,771
Recurring | State and political subdivision
Assets [Abstract]
Debt Securities, Available-for-sale	3,990	4,098
Recurring | ABS
Assets [Abstract]
Debt Securities, Available-for-sale	1,978	1,796
Recurring | CMBS
Assets [Abstract]
Debt Securities, Available-for-sale	4,145	3,291
Recurring | Foreign government
Assets [Abstract]
Debt Securities, Available-for-sale	1,353	1,267
Recurring | Level 1
Assets [Abstract]
Debt Securities, Available-for-sale	3,699	8,002
Available-for-sale Securities, Equity Securities	15	18
Short-term Investments	56	135
Real Estate Investments, Joint Ventures	0
Other limited partnership interests	0
Derivative assets	1	16
Embedded derivatives within asset host contracts	0	0
Separate account assets	202	410
Total assets	3,973	8,581
Liabilities [Abstract]
Derivative liabilities	1	0
Embedded derivatives within liability host contracts	0	0
Total liabilities	1	0
Recurring | Level 1 | Interest rate contracts
Assets [Abstract]
Derivative assets	0	1
Liabilities [Abstract]
Derivative liabilities	0	0
Recurring | Level 1 | Foreign currency exchange rate contracts
Assets [Abstract]
Derivative assets	0	0
Liabilities [Abstract]
Derivative liabilities	0	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	1	15
Liabilities [Abstract]
Derivative liabilities	1	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	3,699	8,002
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 | 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 1 | Foreign government
Assets [Abstract]
Debt Securities, Available-for-sale	0	0
Recurring | Level 2
Assets [Abstract]
Debt Securities, Available-for-sale	54,070	52,167
Available-for-sale Securities, Equity Securities	13	19
Short-term Investments	60	120
Real Estate Investments, Joint Ventures	0
Other limited partnership interests	0
Derivative assets	1,683	2,069
Embedded derivatives within asset host contracts	0	0
Separate account assets	103,692	109,741
Total assets	159,611	164,231
Liabilities [Abstract]
Derivative liabilities	2,853	2,691
Embedded derivatives within liability host contracts	0	0
Total liabilities	2,856	2,702
Recurring | Level 2 | Interest rate contracts
Assets [Abstract]
Derivative assets	629	1,111
Liabilities [Abstract]
Derivative liabilities	1,044	837
Recurring | Level 2 | Foreign currency exchange rate contracts
Assets [Abstract]
Derivative assets	176	155
Liabilities [Abstract]
Derivative liabilities	92	117
Recurring | Level 2 | Credit contracts
Assets [Abstract]
Derivative assets	24	30
Liabilities [Abstract]
Derivative liabilities	1	1
Recurring | Level 2 | Equity market contracts
Assets [Abstract]
Derivative assets	854	773
Liabilities [Abstract]
Derivative liabilities	1,716	1,736
Recurring | Level 2 | U.S. corporate
Assets [Abstract]
Debt Securities, Available-for-sale	22,820	21,491
Recurring | Level 2 | U.S. government and agency
Assets [Abstract]
Debt Securities, Available-for-sale	6,806	7,911
Recurring | Level 2 | RMBS
Assets [Abstract]
Debt Securities, Available-for-sale	7,129	6,836
Recurring | Level 2 | Foreign corporate
Assets [Abstract]
Debt Securities, Available-for-sale	6,040	5,723
Recurring | Level 2 | State and political subdivision
Assets [Abstract]
Debt Securities, Available-for-sale	3,990	4,098
Recurring | Level 2 | ABS
Assets [Abstract]
Debt Securities, Available-for-sale	1,917	1,691
Recurring | Level 2 | CMBS
Assets [Abstract]
Debt Securities, Available-for-sale	4,015	3,155
Recurring | Level 2 | Foreign government
Assets [Abstract]
Debt Securities, Available-for-sale	1,353	1,262
Recurring | Level 3
Assets [Abstract]
Debt Securities, Available-for-sale	2,858	3,164
Available-for-sale Securities, Equity Securities	122	124
Short-term Investments	0	14
Real Estate Investments, Joint Ventures	15
Other limited partnership interests	25
Derivative assets	162	159
Embedded derivatives within asset host contracts	166	227
Separate account assets	4	5
Total assets	3,352	3,693
Liabilities [Abstract]
Derivative liabilities	450	438
Embedded derivatives within liability host contracts	1,831	2,234
Total liabilities	2,281	2,672
Recurring | Level 3 | Interest rate contracts
Assets [Abstract]
Derivative assets	0	0
Liabilities [Abstract]
Derivative liabilities	0	0
Recurring | Level 3 | Foreign currency exchange rate contracts
Assets [Abstract]
Derivative assets	0	0
Liabilities [Abstract]
Derivative liabilities	1	1
Recurring | Level 3 | Credit contracts
Assets [Abstract]
Derivative assets	10	10
Liabilities [Abstract]
Derivative liabilities	0	0
Recurring | Level 3 | Equity market contracts
Assets [Abstract]
Derivative assets	152	149
Liabilities [Abstract]
Derivative liabilities	449	437
Recurring | Level 3 | U.S. corporate
Assets [Abstract]
Debt Securities, Available-for-sale	584	889
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	1,078	981
Recurring | Level 3 | Foreign corporate
Assets [Abstract]
Debt Securities, Available-for-sale	1,005	1,048
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	61	105
Recurring | Level 3 | CMBS
Assets [Abstract]
Debt Securities, Available-for-sale	130	136
Recurring | Level 3 | Foreign government
Assets [Abstract]
Debt Securities, Available-for-sale	0	5
Variable Interest Entity, Primary Beneficiary
Assets [Abstract]
Mortgage Loans on Real Estate, Commerical and Consumer Net	93	115
Liabilities [Abstract]
Long-term debt, at estimated fair value, relating to variable interest entities	3	11
Variable Interest Entity, Primary Beneficiary | Recurring
Assets [Abstract]
Mortgage Loans on Real Estate, Commerical and Consumer Net	93	115
Liabilities [Abstract]
Long-term debt, at estimated fair value, relating to variable interest entities	3	11
Variable Interest Entity, Primary Beneficiary | Recurring | Level 1
Assets [Abstract]
Mortgage Loans on Real Estate, Commerical and Consumer Net	0	0
Liabilities [Abstract]
Long-term debt, at estimated fair value, relating to variable interest entities	0	0
Variable Interest Entity, Primary Beneficiary | Recurring | Level 2
Assets [Abstract]
Mortgage Loans on Real Estate, Commerical and Consumer Net	93	115
Liabilities [Abstract]
Long-term debt, at estimated fair value, relating to variable interest entities	3	11
Variable Interest Entity, Primary Beneficiary | Recurring | Level 3
Assets [Abstract]
Mortgage Loans on Real Estate, Commerical and Consumer Net	0	0
Liabilities [Abstract]
Long-term debt, at estimated fair value, relating to variable interest entities	$ 0	$ 0