Investments (Trading Account Assets Supporting Insurance Liabilities) (Details) - USD ($) $ in Millions		Sep. 30, 2015	Dec. 31, 2014
Major Types Of Investment Securities [Line Items]
Amortized Cost		$ 19,925	$ 19,263
Fair Value	[1]	20,408	20,263
Fixed Maturities
Major Types Of Investment Securities [Line Items]
Amortized Cost		17,938	18,171
Fair Value		18,285	18,881
Equity securities
Major Types Of Investment Securities [Line Items]
Amortized Cost		1,016	896
Fair Value		1,153	1,186
Short-term investments and cash equivalents
Major Types Of Investment Securities [Line Items]
Amortized Cost		971	196
Fair Value		970	196
Corporate securities | Fixed Maturities
Major Types Of Investment Securities [Line Items]
Amortized Cost		12,282	11,922
Fair Value		12,483	12,439
Commercial mortgage-backed securities | Fixed Maturities
Major Types Of Investment Securities [Line Items]
Amortized Cost		1,798	2,505
Fair Value		1,836	2,546
Residential mortgage-backed securities | Fixed Maturities
Major Types Of Investment Securities [Line Items]
Amortized Cost		1,472	1,640
Fair Value		1,504	1,676
Asset-backed securities | Fixed Maturities
Major Types Of Investment Securities [Line Items]
Amortized Cost		1,417	1,180
Fair Value		1,432	1,198
Foreign government bonds | Fixed Maturities
Major Types Of Investment Securities [Line Items]
Amortized Cost		659	621
Fair Value		674	650
U.S. government authorities and agencies and obligations of U.S. states | Fixed Maturities
Major Types Of Investment Securities [Line Items]
Amortized Cost		310	303
Fair Value		$ 356	$ 372

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