Investments (Trading Account Assets Supporting Insurance Liabilities) (Details) - USD ($) $ in Millions		Dec. 31, 2015	Dec. 31, 2014
Major Types Of Investment Securities [Line Items]
Amortized Cost		$ 20,164	$ 19,263
Fair Value	[1]	20,522	20,263
Short-term investments and cash equivalents
Major Types Of Investment Securities [Line Items]
Amortized Cost		765	196
Fair Value		765	196
Fixed maturities
Major Types Of Investment Securities [Line Items]
Amortized Cost		18,369	18,171
Fair Value		18,503	18,881
Fixed maturities | Corporate securities
Major Types Of Investment Securities [Line Items]
Amortized Cost		12,797	11,922
Fair Value		12,851	12,439
Fixed maturities | Commercial mortgage-backed securities
Major Types Of Investment Securities [Line Items]
Amortized Cost		1,860	2,505
Fair Value		1,862	2,546
Fixed maturities | Residential mortgage-backed securities
Major Types Of Investment Securities [Line Items]
Amortized Cost		1,411	1,640
Fair Value		1,428	1,676
Fixed maturities | Asset-backed securities
Major Types Of Investment Securities [Line Items]
Amortized Cost		1,295	1,180
Fair Value		1,299	1,198
Fixed maturities | Foreign government bonds
Major Types Of Investment Securities [Line Items]
Amortized Cost		680	621
Fair Value		694	650
Fixed maturities | U.S. government authorities and agencies and obligations of U.S. states
Major Types Of Investment Securities [Line Items]
Amortized Cost		326	303
Fair Value		369	372
Equity securities
Major Types Of Investment Securities [Line Items]
Amortized Cost		1,030	896
Fair Value		$ 1,254	$ 1,186

[1] See Note 5 for details of balances associated with variable interest entities.