Fair Value (Recurring Fair Value Measurements) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Assets [Abstract]
Available-for-sale Securities, Debt Securities	$ 63,333	$ 59,899
Available-for-sale Securities, Equity Securities	232	300
Short-term investments, principally at estimated fair value	269	1,272
Mortgage Loans on Real Estate	10,640	9,290
Derivative assets	2,244	3,603
Net embedded derivatives within asset host contracts	175	360
Separate account assets	110,156	105,346
Liabilities [Abstract]
Derivative liabilities	3,129	3,883
Net embedded derivatives within liability host contracts	2,234	3,170
Long-term debt, at estimated fair value, relating to variable interest entities	46	1,904
Consolidated Securitization Entities
Assets [Abstract]
Mortgage Loans on Real Estate	115	136
Liabilities [Abstract]
Long-term debt, at estimated fair value, relating to variable interest entities	11	23
Recurring
Assets [Abstract]
Available-for-sale Securities, Debt Securities	63,333	59,899
Available-for-sale Securities, Equity Securities	232	300
Short-term investments, principally at estimated fair value	269	1,272
Derivative assets	2,244	3,603
Net embedded derivatives within asset host contracts	227	409
Separate account assets	110,156	105,346
Total assets	176,576	170,965
Liabilities [Abstract]
Derivative liabilities	3,129	3,883
Net embedded derivatives within liability host contracts	2,234	3,170
Total liabilities	5,374	7,076
Recurring | Consolidated Securitization Entities
Assets [Abstract]
Mortgage Loans on Real Estate	115	136
Liabilities [Abstract]
Long-term debt, at estimated fair value, relating to variable interest entities	11	23
Recurring | Interest rate
Assets [Abstract]
Derivative assets	1,112	2,151
Liabilities [Abstract]
Derivative liabilities	837	2,301
Recurring | Foreign currency exchange rate
Assets [Abstract]
Derivative assets	155	348
Liabilities [Abstract]
Derivative liabilities	118	14
Recurring | Credit
Assets [Abstract]
Derivative assets	40	28
Liabilities [Abstract]
Derivative liabilities	1
Recurring | Equity market
Assets [Abstract]
Derivative assets	937	1,076
Liabilities [Abstract]
Derivative liabilities	2,173	1,568
Recurring | U.S. corporate
Assets [Abstract]
Available-for-sale Securities, Debt Securities	22,380	21,665
Recurring | U.S. government and agency
Assets [Abstract]
Available-for-sale Securities, Debt Securities	15,913	12,916
Recurring | RMBS
Assets [Abstract]
Available-for-sale Securities, Debt Securities	7,817	7,940
Recurring | Foreign corporate
Assets [Abstract]
Available-for-sale Securities, Debt Securities	6,771	6,123
Recurring | State and political subdivision
Assets [Abstract]
Available-for-sale Securities, Debt Securities	4,098	3,858
Recurring | ABS
Assets [Abstract]
Available-for-sale Securities, Debt Securities	1,796	2,598
Recurring | Foreign government
Assets [Abstract]
Available-for-sale Securities, Debt Securities	1,267	1,103
Recurring | CMBS
Assets [Abstract]
Available-for-sale Securities, Debt Securities	3,291	3,696
Recurring | Level 1
Assets [Abstract]
Available-for-sale Securities, Debt Securities	8,002	6,110
Available-for-sale Securities, Equity Securities	18	39
Short-term investments, principally at estimated fair value	135	702
Derivative assets	16	46
Net embedded derivatives within asset host contracts	0	0
Separate account assets	410	720
Total assets	8,581	7,617
Liabilities [Abstract]
Derivative liabilities	0	0
Net embedded derivatives within liability host contracts	0	0
Total liabilities	0	0
Recurring | Level 1 | Consolidated Securitization Entities
Assets [Abstract]
Mortgage Loans on Real Estate	0	0
Liabilities [Abstract]
Long-term debt, at estimated fair value, relating to variable interest entities	0	0
Recurring | Level 1 | Interest rate
Assets [Abstract]
Derivative assets	1	9
Liabilities [Abstract]
Derivative liabilities	0	0
Recurring | Level 1 | Foreign currency exchange rate
Assets [Abstract]
Derivative assets	0	0
Liabilities [Abstract]
Derivative liabilities	0	0
Recurring | Level 1 | Credit
Assets [Abstract]
Derivative assets	0	0
Liabilities [Abstract]
Derivative liabilities	0
Recurring | Level 1 | Equity market
Assets [Abstract]
Derivative assets	15	37
Liabilities [Abstract]
Derivative liabilities	0	0
Recurring | Level 1 | U.S. corporate
Assets [Abstract]
Available-for-sale Securities, Debt Securities	0	0
Recurring | Level 1 | U.S. government and agency
Assets [Abstract]
Available-for-sale Securities, Debt Securities	8,002	6,110
Recurring | Level 1 | RMBS
Assets [Abstract]
Available-for-sale Securities, Debt Securities	0	0
Recurring | Level 1 | Foreign corporate
Assets [Abstract]
Available-for-sale Securities, Debt Securities	0	0
Recurring | Level 1 | State and political subdivision
Assets [Abstract]
Available-for-sale Securities, Debt Securities	0	0
Recurring | Level 1 | ABS
Assets [Abstract]
Available-for-sale Securities, Debt Securities	0	0
Recurring | Level 1 | Foreign government
Assets [Abstract]
Available-for-sale Securities, Debt Securities	0	0
Recurring | Level 1 | CMBS
Assets [Abstract]
Available-for-sale Securities, Debt Securities	0	0
Recurring | Level 2
Assets [Abstract]
Available-for-sale Securities, Debt Securities	52,167	49,767
Available-for-sale Securities, Equity Securities	90	124
Short-term investments, principally at estimated fair value	120	568
Derivative assets	2,069	3,370
Net embedded derivatives within asset host contracts	0	0
Separate account assets	109,741	104,616
Total assets	164,302	158,581
Liabilities [Abstract]
Derivative liabilities	2,691	2,742
Net embedded derivatives within liability host contracts	0	0
Total liabilities	2,702	2,765
Recurring | Level 2 | Consolidated Securitization Entities
Assets [Abstract]
Mortgage Loans on Real Estate	115	136
Liabilities [Abstract]
Long-term debt, at estimated fair value, relating to variable interest entities	11	23
Recurring | Level 2 | Interest rate
Assets [Abstract]
Derivative assets	1,111	2,142
Liabilities [Abstract]
Derivative liabilities	837	1,690
Recurring | Level 2 | Foreign currency exchange rate
Assets [Abstract]
Derivative assets	155	348
Liabilities [Abstract]
Derivative liabilities	117	14
Recurring | Level 2 | Credit
Assets [Abstract]
Derivative assets	30	20
Liabilities [Abstract]
Derivative liabilities	1
Recurring | Level 2 | Equity market
Assets [Abstract]
Derivative assets	773	860
Liabilities [Abstract]
Derivative liabilities	1,736	1,038
Recurring | Level 2 | U.S. corporate
Assets [Abstract]
Available-for-sale Securities, Debt Securities	21,491	20,221
Recurring | Level 2 | U.S. government and agency
Assets [Abstract]
Available-for-sale Securities, Debt Securities	7,911	6,806
Recurring | Level 2 | RMBS
Assets [Abstract]
Available-for-sale Securities, Debt Securities	6,836	6,627
Recurring | Level 2 | Foreign corporate
Assets [Abstract]
Available-for-sale Securities, Debt Securities	5,723	5,257
Recurring | Level 2 | State and political subdivision
Assets [Abstract]
Available-for-sale Securities, Debt Securities	4,098	3,841
Recurring | Level 2 | ABS
Assets [Abstract]
Available-for-sale Securities, Debt Securities	1,691	2,383
Recurring | Level 2 | Foreign government
Assets [Abstract]
Available-for-sale Securities, Debt Securities	1,262	1,103
Recurring | Level 2 | CMBS
Assets [Abstract]
Available-for-sale Securities, Debt Securities	3,155	3,529
Recurring | Level 3
Assets [Abstract]
Available-for-sale Securities, Debt Securities	3,164	4,022
Available-for-sale Securities, Equity Securities	124	137
Short-term investments, principally at estimated fair value	14	2
Derivative assets	159	187
Net embedded derivatives within asset host contracts	227	409
Separate account assets	5	10
Total assets	3,693	4,767
Liabilities [Abstract]
Derivative liabilities	438	1,141
Net embedded derivatives within liability host contracts	2,234	3,170
Total liabilities	2,672	4,311
Recurring | Level 3 | Consolidated Securitization Entities
Assets [Abstract]
Mortgage Loans on Real Estate	0	0
Liabilities [Abstract]
Long-term debt, at estimated fair value, relating to variable interest entities	0	0
Recurring | Level 3 | Interest rate
Assets [Abstract]
Derivative assets	0	0
Liabilities [Abstract]
Derivative liabilities	0	611
Recurring | Level 3 | Foreign currency exchange rate
Assets [Abstract]
Derivative assets	0	0
Liabilities [Abstract]
Derivative liabilities	1	0
Recurring | Level 3 | Credit
Assets [Abstract]
Derivative assets	10	8
Liabilities [Abstract]
Derivative liabilities	0
Recurring | Level 3 | Equity market
Assets [Abstract]
Derivative assets	149	179
Liabilities [Abstract]
Derivative liabilities	437	530
Recurring | Level 3 | U.S. corporate
Assets [Abstract]
Available-for-sale Securities, Debt Securities	889	1,444
Recurring | Level 3 | U.S. government and agency
Assets [Abstract]
Available-for-sale Securities, Debt Securities	0	0
Recurring | Level 3 | RMBS
Assets [Abstract]
Available-for-sale Securities, Debt Securities	981	1,313
Recurring | Level 3 | Foreign corporate
Assets [Abstract]
Available-for-sale Securities, Debt Securities	1,048	866
Recurring | Level 3 | State and political subdivision
Assets [Abstract]
Available-for-sale Securities, Debt Securities	0	17
Recurring | Level 3 | ABS
Assets [Abstract]
Available-for-sale Securities, Debt Securities	105	215
Recurring | Level 3 | Foreign government
Assets [Abstract]
Available-for-sale Securities, Debt Securities	5	0
Recurring | Level 3 | CMBS
Assets [Abstract]
Available-for-sale Securities, Debt Securities	$ 136	$ 167