Investments (Summary of fixed maturity and equity securities) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Cost or Amortized Cost	$ 39,318	$ 38,398
Gross Unrealized Gains	2,673	4,639
Gross Unrealized Losses	518	155
Estimated Fair Value	41,473	42,882
Corporate and other bonds [Member]
Cost or Amortized Cost	19,616	19,530
Gross Unrealized Gains	1,695	2,698
Gross Unrealized Losses	151	21
Estimated Fair Value	21,160	22,207
Unrealized OTTI Losses (Gains)
States, municipalities and political subdivisions [Member]
Cost or Amortized Cost	11,000	9,372
Gross Unrealized Gains	672	1,455
Gross Unrealized Losses	233	44
Estimated Fair Value	11,439	10,783
Unrealized OTTI Losses (Gains)
Residential mortgage-backed [Member]
Cost or Amortized Cost	4,779	5,745
Gross Unrealized Gains	141	246
Gross Unrealized Losses	101	71
Estimated Fair Value	4,819	5,920
Unrealized OTTI Losses (Gains)	(33)	(28)
Commercial mortgage-backed [Member]
Cost or Amortized Cost	1,942	1,692
Gross Unrealized Gains	99	147
Gross Unrealized Losses	24	17
Estimated Fair Value	2,017	1,822
Unrealized OTTI Losses (Gains)	(3)	(3)
Other asset-backed [Member]
Cost or Amortized Cost	942	929
Gross Unrealized Gains	16	23
Gross Unrealized Losses	2
Estimated Fair Value	956	952
Unrealized OTTI Losses (Gains)
Total asset-backed [Member]
Cost or Amortized Cost	7,663	8,366
Gross Unrealized Gains	256	416
Gross Unrealized Losses	127	88
Estimated Fair Value	7,792	8,694
Unrealized OTTI Losses (Gains)	(36)	(31)
U.S. Treasury and obligations of government-sponsored enterprises [Member]
Cost or Amortized Cost	166	172
Gross Unrealized Gains	8	11
Gross Unrealized Losses	1	1
Estimated Fair Value	173	182
Unrealized OTTI Losses (Gains)
Foreign government [Member]
Cost or Amortized Cost	547	588
Gross Unrealized Gains	17	25
Gross Unrealized Losses	3
Estimated Fair Value	561	613
Unrealized OTTI Losses (Gains)
Redeemable preferred stock [Member]
Cost or Amortized Cost	94	113
Gross Unrealized Gains	12	13
Gross Unrealized Losses		1
Estimated Fair Value	106	125
Unrealized OTTI Losses (Gains)
Total fixed maturity securities available-for-sale [Member]
Cost or Amortized Cost	39,086	38,141
Gross Unrealized Gains	2,660	4,618
Gross Unrealized Losses	515	155
Estimated Fair Value	41,231	42,604
Unrealized OTTI Losses (Gains)	(36)	(31)
Total fixed maturity securities trading [Member]
Cost or Amortized Cost, Trading Securities	43	29
Gross Unrealized Gains, Trading Securities
Gross Unrealized Losses, Trading Securities
Estimated Fair Value, Trading Securities	43	29
Common stock [Member]
Cost or Amortized Cost	41	38
Gross Unrealized Gains	12	14
Gross Unrealized Losses
Estimated Fair Value	53	52
Preferred stock [Member]
Cost or Amortized Cost	148	190
Gross Unrealized Gains	1	7
Gross Unrealized Losses	3
Estimated Fair Value	146	197
Total equity securities available-for-sale [Member]
Cost or Amortized Cost	189	228
Gross Unrealized Gains	13	21
Gross Unrealized Losses	3
Estimated Fair Value	$ 199	$ 249