Fair Value (Recurring Fair Value Measurements) (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Assets [Abstract]
Debt Securities, Available-for-sale	$ 60,753	$ 63,333
Available-for-sale Securities, Equity Securities	153	161
Short-term Investments	115	269
Mortgage Loans on Real Estate, Commerical and Consumer Net	12,237	10,640
Derivative assets	2,045	2,244
Embedded derivatives within asset host contracts	184	175
Separate account assets	103,801	110,156
Liabilities [Abstract]
Derivative liabilities	3,223	3,129
Embedded derivatives within liability host contracts	1,682	2,234
Long-term debt, at estimated fair value, relating to variable interest entities	40	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	60,753	63,333
Available-for-sale Securities, Equity Securities	153	161
Short-term Investments	115	269
Real Estate Investments, Joint Ventures	17
Other limited partnership interests	24
Derivative assets	2,045	2,244
Embedded derivatives within asset host contracts	184	227
Separate account assets	103,801	110,156
Total assets	167,188	176,505
Liabilities [Abstract]
Derivative liabilities	3,223	3,129
Embedded derivatives within liability host contracts	1,682	2,234
Total liabilities	4,910	5,374
Recurring | Interest rate contracts
Assets [Abstract]
Derivative assets	762	1,112
Liabilities [Abstract]
Derivative liabilities	985	837
Recurring | Foreign currency exchange rate contracts
Assets [Abstract]
Derivative assets	178	155
Liabilities [Abstract]
Derivative liabilities	93	118
Recurring | Credit contracts
Assets [Abstract]
Derivative assets	28	40
Liabilities [Abstract]
Derivative liabilities	2	1
Recurring | Equity market contracts
Assets [Abstract]
Derivative assets	1,077	937
Liabilities [Abstract]
Derivative liabilities	2,143	2,173
Recurring | U.S. corporate
Assets [Abstract]
Debt Securities, Available-for-sale	22,963	22,380
Recurring | U.S. government and agency
Assets [Abstract]
Debt Securities, Available-for-sale	12,078	15,913
Recurring | RMBS
Assets [Abstract]
Debt Securities, Available-for-sale	7,695	7,817
Recurring | Foreign corporate
Assets [Abstract]
Debt Securities, Available-for-sale	6,746	6,771
Recurring | State and political subdivision
Assets [Abstract]
Debt Securities, Available-for-sale	3,995	4,098
Recurring | ABS
Assets [Abstract]
Debt Securities, Available-for-sale	2,050	1,796
Recurring | CMBS
Assets [Abstract]
Debt Securities, Available-for-sale	3,891	3,291
Recurring | Foreign government
Assets [Abstract]
Debt Securities, Available-for-sale	1,335	1,267
Recurring | Level 1
Assets [Abstract]
Debt Securities, Available-for-sale	4,634	8,002
Available-for-sale Securities, Equity Securities	15	18
Short-term Investments	53	135
Real Estate Investments, Joint Ventures	0
Other limited partnership interests	0
Derivative assets	0	16
Embedded derivatives within asset host contracts	0	0
Separate account assets	182	410
Total assets	4,884	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	0	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	4,634	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	53,035	52,167
Available-for-sale Securities, Equity Securities	18	19
Short-term Investments	62	120
Real Estate Investments, Joint Ventures	0
Other limited partnership interests	0
Derivative assets	1,894	2,069
Embedded derivatives within asset host contracts	0	0
Separate account assets	103,615	109,741
Total assets	158,720	164,231
Liabilities [Abstract]
Derivative liabilities	2,787	2,691
Embedded derivatives within liability host contracts	0	0
Total liabilities	2,792	2,702
Recurring | Level 2 | Interest rate contracts
Assets [Abstract]
Derivative assets	762	1,111
Liabilities [Abstract]
Derivative liabilities	985	837
Recurring | Level 2 | Foreign currency exchange rate contracts
Assets [Abstract]
Derivative assets	178	155
Liabilities [Abstract]
Derivative liabilities	92	117
Recurring | Level 2 | Credit contracts
Assets [Abstract]
Derivative assets	20	30
Liabilities [Abstract]
Derivative liabilities	2	1
Recurring | Level 2 | Equity market contracts
Assets [Abstract]
Derivative assets	934	773
Liabilities [Abstract]
Derivative liabilities	1,708	1,736
Recurring | Level 2 | U.S. corporate
Assets [Abstract]
Debt Securities, Available-for-sale	22,144	21,491
Recurring | Level 2 | U.S. government and agency
Assets [Abstract]
Debt Securities, Available-for-sale	7,444	7,911
Recurring | Level 2 | RMBS
Assets [Abstract]
Debt Securities, Available-for-sale	6,766	6,836
Recurring | Level 2 | Foreign corporate
Assets [Abstract]
Debt Securities, Available-for-sale	5,750	5,723
Recurring | Level 2 | State and political subdivision
Assets [Abstract]
Debt Securities, Available-for-sale	3,987	4,098
Recurring | Level 2 | ABS
Assets [Abstract]
Debt Securities, Available-for-sale	1,896	1,691
Recurring | Level 2 | CMBS
Assets [Abstract]
Debt Securities, Available-for-sale	3,713	3,155
Recurring | Level 2 | Foreign government
Assets [Abstract]
Debt Securities, Available-for-sale	1,335	1,262
Recurring | Level 3
Assets [Abstract]
Debt Securities, Available-for-sale	3,084	3,164
Available-for-sale Securities, Equity Securities	120	124
Short-term Investments	0	14
Real Estate Investments, Joint Ventures	17
Other limited partnership interests	24
Derivative assets	151	159
Embedded derivatives within asset host contracts	184	227
Separate account assets	4	5
Total assets	3,584	3,693
Liabilities [Abstract]
Derivative liabilities	435	438
Embedded derivatives within liability host contracts	1,682	2,234
Total liabilities	2,117	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	8	10
Liabilities [Abstract]
Derivative liabilities	0	0
Recurring | Level 3 | Equity market contracts
Assets [Abstract]
Derivative assets	143	149
Liabilities [Abstract]
Derivative liabilities	434	437
Recurring | Level 3 | U.S. corporate
Assets [Abstract]
Debt Securities, Available-for-sale	819	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	929	981
Recurring | Level 3 | Foreign corporate
Assets [Abstract]
Debt Securities, Available-for-sale	996	1,048
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	154	105
Recurring | Level 3 | CMBS
Assets [Abstract]
Debt Securities, Available-for-sale	178	136
Recurring | Level 3 | Foreign government
Assets [Abstract]
Debt Securities, Available-for-sale	0	5
Variable Interest Entity, Primary Beneficiary [Member]
Assets [Abstract]
Mortgage Loans on Real Estate, Commerical and Consumer Net	96	115
Liabilities [Abstract]
Long-term debt, at estimated fair value, relating to variable interest entities	5	11
Variable Interest Entity, Primary Beneficiary [Member] | Recurring
Assets [Abstract]
Mortgage Loans on Real Estate, Commerical and Consumer Net	96	115
Liabilities [Abstract]
Long-term debt, at estimated fair value, relating to variable interest entities	5	11
Variable Interest Entity, Primary Beneficiary [Member] | 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 [Member] | Recurring | Level 2
Assets [Abstract]
Mortgage Loans on Real Estate, Commerical and Consumer Net	96	115
Liabilities [Abstract]
Long-term debt, at estimated fair value, relating to variable interest entities	5	11
Variable Interest Entity, Primary Beneficiary [Member] | 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