Investments (Securities in a gross unrealized loss position) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Estimated Fair Value, Less Than 12 Months	$ 8,062	$ 1,819
Gross Unrealized Losses, Less than 12 Months	394	27
Estimated Fair Value, 12 Months or Longer	533	866
Gross Unrealized Losses, 12 Months or Longer	124	128
Estimated Fair Value, Total	8,595	2,685
Gross Unrealized Losses, Total	518	155
Corporate and other bonds [Member]
Estimated Fair Value, Less Than 12 Months	3,521	846
Gross Unrealized Losses, Less than 12 Months	146	13
Estimated Fair Value, 12 Months or Longer	45	108
Gross Unrealized Losses, 12 Months or Longer	5	8
Estimated Fair Value, Total	3,566	954
Gross Unrealized Losses, Total	151	21
States, municipalities and political subdivisions [Member]
Estimated Fair Value, Less Than 12 Months	2,413	254
Gross Unrealized Losses, Less than 12 Months	179	5
Estimated Fair Value, 12 Months or Longer	122	165
Gross Unrealized Losses, 12 Months or Longer	54	39
Estimated Fair Value, Total	2,535	419
Gross Unrealized Losses, Total	233	44
Residential mortgage-backed [Member]
Estimated Fair Value, Less Than 12 Months	1,289	583
Gross Unrealized Losses, Less than 12 Months	40	5
Estimated Fair Value, 12 Months or Longer	287	452
Gross Unrealized Losses, 12 Months or Longer	61	66
Estimated Fair Value, Total	1,576	1,035
Gross Unrealized Losses, Total	101	71
Commercial mortgage-backed [Member]
Estimated Fair Value, Less Than 12 Months	449	85
Gross Unrealized Losses, Less than 12 Months	20	2
Estimated Fair Value, 12 Months or Longer	79	141
Gross Unrealized Losses, 12 Months or Longer	4	15
Estimated Fair Value, Total	528	226
Gross Unrealized Losses, Total	24	17
Other asset-backed [Member]
Estimated Fair Value, Less Than 12 Months	207
Gross Unrealized Losses, Less than 12 Months	2
Estimated Fair Value, 12 Months or Longer
Gross Unrealized Losses, 12 Months or Longer
Estimated Fair Value, Total	207
Gross Unrealized Losses, Total	2
Total asset-backed [Member]
Estimated Fair Value, Less Than 12 Months	1,945	668
Gross Unrealized Losses, Less than 12 Months	62	7
Estimated Fair Value, 12 Months or Longer	366	593
Gross Unrealized Losses, 12 Months or Longer	65	81
Estimated Fair Value, Total	2,311	1,261
Gross Unrealized Losses, Total	127	88
U.S. Treasury and obligations of government-sponsored enterprises [Member]
Estimated Fair Value, Less Than 12 Months	21	23
Gross Unrealized Losses, Less than 12 Months	1	1
Estimated Fair Value, 12 Months or Longer
Gross Unrealized Losses, 12 Months or Longer
Estimated Fair Value, Total	21	23
Gross Unrealized Losses, Total	1	1
Foreign government [Member]
Estimated Fair Value, Less Than 12 Months	76
Gross Unrealized Losses, Less than 12 Months	3
Estimated Fair Value, 12 Months or Longer
Gross Unrealized Losses, 12 Months or Longer
Estimated Fair Value, Total	76
Gross Unrealized Losses, Total	3
Total fixed maturity securities available-for-sale [Member]
Estimated Fair Value, Less Than 12 Months	7,976
Gross Unrealized Losses, Less than 12 Months	391
Estimated Fair Value, 12 Months or Longer	533
Gross Unrealized Losses, 12 Months or Longer	124
Estimated Fair Value, Total	8,509
Gross Unrealized Losses, Total	515
Preferred stock [Member]
Estimated Fair Value, Less Than 12 Months	86
Gross Unrealized Losses, Less than 12 Months	3
Estimated Fair Value, 12 Months or Longer
Gross Unrealized Losses, 12 Months or Longer
Estimated Fair Value, Total	86
Gross Unrealized Losses, Total	3
Redeemable preferred stock [Member]
Estimated Fair Value, Less Than 12 Months		28
Gross Unrealized Losses, Less than 12 Months		1
Estimated Fair Value, 12 Months or Longer
Gross Unrealized Losses, 12 Months or Longer
Estimated Fair Value, Total		28
Gross Unrealized Losses, Total		$ 1