Investments (Summary of fixed maturity and equity securities) (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Cost or Amortized Cost	$ 39,113	$ 38,398
Gross Unrealized Gains	2,957	4,639
Gross Unrealized Losses	440	155
Estimated Fair Value	41,630	42,882
Corporate and other bonds [Member]
Cost or Amortized Cost	20,079	19,530
Gross Unrealized Gains	1,826	2,698
Gross Unrealized Losses	147	21
Estimated Fair Value	21,758	22,207
Unrealized OTTI Losses (Gains)
States, municipalities and political subdivisions [Member]
Cost or Amortized Cost	10,098	9,372
Gross Unrealized Gains	814	1,455
Gross Unrealized Losses	173	44
Estimated Fair Value	10,739	10,783
Unrealized OTTI Losses (Gains)
Residential mortgage-backed [Member]
Cost or Amortized Cost	5,031	5,745
Gross Unrealized Gains	153	246
Gross Unrealized Losses	88	71
Estimated Fair Value	5,096	5,920
Unrealized OTTI Losses (Gains)	(37)	(28)
Commercial mortgage-backed [Member]
Cost or Amortized Cost	1,941	1,692
Gross Unrealized Gains	95	147
Gross Unrealized Losses	27	17
Estimated Fair Value	2,009	1,822
Unrealized OTTI Losses (Gains)	(3)	(3)
Other asset-backed [Member]
Cost or Amortized Cost	933	929
Gross Unrealized Gains	16	23
Gross Unrealized Losses	2
Estimated Fair Value	947	952
Unrealized OTTI Losses (Gains)
Total asset-backed [Member]
Cost or Amortized Cost	7,905	8,366
Gross Unrealized Gains	264	416
Gross Unrealized Losses	117	88
Estimated Fair Value	8,052	8,694
Unrealized OTTI Losses (Gains)	(40)	(31)
U.S. Treasury and obligations of government-sponsored enterprises [Member]
Cost or Amortized Cost	167	172
Gross Unrealized Gains	9	11
Gross Unrealized Losses		1
Estimated Fair Value	176	182
Unrealized OTTI Losses (Gains)
Foreign government [Member]
Cost or Amortized Cost	528	588
Gross Unrealized Gains	17	25
Gross Unrealized Losses	1
Estimated Fair Value	544	613
Unrealized OTTI Losses (Gains)
Redeemable preferred stock [Member]
Cost or Amortized Cost	121	113
Gross Unrealized Gains	13	13
Gross Unrealized Losses	2	1
Estimated Fair Value	132	125
Unrealized OTTI Losses (Gains)
Total fixed maturity securities available-for-sale [Member]
Cost or Amortized Cost	38,898	38,141
Gross Unrealized Gains	2,943	4,618
Gross Unrealized Losses	440	155
Estimated Fair Value	41,401	42,604
Unrealized OTTI Losses (Gains)	(40)	(31)
Total fixed maturity securities trading [Member]
Cost or Amortized Cost, Trading Securities	30	29
Gross Unrealized Gains, Trading Securities
Gross Unrealized Losses, Trading Securities
Estimated Fair Value, Trading Securities	30	29
Common stock [Member]
Cost or Amortized Cost	47	38
Gross Unrealized Gains	10	14
Gross Unrealized Losses
Estimated Fair Value	57	52
Preferred stock [Member]
Cost or Amortized Cost	138	190
Gross Unrealized Gains	4	7
Gross Unrealized Losses
Estimated Fair Value	142	197
Total equity securities available-for-sale [Member]
Cost or Amortized Cost	185	228
Gross Unrealized Gains	14	21
Gross Unrealized Losses
Estimated Fair Value	$ 199	$ 249