Investments (Summary of fixed maturity and equity securities) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2014	Dec. 31, 2013
Cost or Amortized Cost	$ 37,076	$ 39,490
Gross Unrealized Gains	2,781	2,460
Gross Unrealized Losses	268	532
Estimated fair value	39,589	41,418
Corporate and other bonds [Member]
Cost or Amortized Cost	17,265	19,352
Gross Unrealized Gains	1,612	1,645
Gross Unrealized Losses	56	135
Estimated fair value	18,821	20,862
Unrealized OTTI Losses (Gains)
States, municipalities and political subdivisions [Member]
Cost or Amortized Cost	11,113	11,281
Gross Unrealized Gains	871	548
Gross Unrealized Losses	129	272
Estimated fair value	11,855	11,557
Unrealized OTTI Losses (Gains)
Residential mortgage-backed [Member]
Cost or Amortized Cost	4,854	4,940
Gross Unrealized Gains	156	123
Gross Unrealized Losses	66	92
Estimated fair value	4,944	4,971
Unrealized OTTI Losses (Gains)	(47)	(37)
Commercial mortgage-backed [Member]
Cost or Amortized Cost	1,974	1,995
Gross Unrealized Gains	92	90
Gross Unrealized Losses	13	22
Estimated fair value	2,053	2,063
Unrealized OTTI Losses (Gains)	(3)	(3)
Other asset-backed [Member]
Cost or Amortized Cost	966	945
Gross Unrealized Gains	12	13
Gross Unrealized Losses	2	3
Estimated fair value	976	955
Unrealized OTTI Losses (Gains)
Total asset-backed [Member]
Cost or Amortized Cost	7,794	7,880
Gross Unrealized Gains	260	226
Gross Unrealized Losses	81	117
Estimated fair value	7,973	7,989
Unrealized OTTI Losses (Gains)	(50)	(40)
U.S. Treasury and obligations of government-sponsored enterprises [Member]
Cost or Amortized Cost	135	139
Gross Unrealized Gains	7	6
Gross Unrealized Losses	1	1
Estimated fair value	141	144
Unrealized OTTI Losses (Gains)
Foreign Government [Member]
Cost or Amortized Cost	559	531
Gross Unrealized Gains	18	15
Gross Unrealized Losses	1	3
Estimated fair value	576	543
Unrealized OTTI Losses (Gains)
Redeemable preferred stock [Member]
Cost or Amortized Cost	32	92
Gross Unrealized Gains	2	10
Gross Unrealized Losses
Estimated fair value	34	102
Unrealized OTTI Losses (Gains)
Total fixed maturity securities available-for-sale [Member]
Cost or Amortized Cost	36,898	39,275
Gross Unrealized Gains	2,770	2,450
Gross Unrealized Losses	268	528
Estimated fair value	39,400	41,197
Unrealized OTTI Losses (Gains)	(50)	(40)
Total fixed maturity securities trading [Member]
Cost or Amortized Cost, Trading Securities	15	36
Gross Unrealized Gains, Trading Securities
Gross Unrealized Losses, Trading Securities
Estimated Fair Value, Trading Securities	15	36
Common stock [Member]
Cost or Amortized Cost	33	36
Gross Unrealized Gains	9	9
Gross Unrealized Losses
Estimated fair value	42	45
Preferred stock [Member]
Cost or Amortized Cost	130	143
Gross Unrealized Gains	2	1
Gross Unrealized Losses		4
Estimated fair value	132	140
Total equity securities available-for-sale [Member]
Cost or Amortized Cost	163	179
Gross Unrealized Gains	11	10
Gross Unrealized Losses		4
Estimated fair value	$ 174	$ 185