Investments (Securities in a gross unrealized loss position) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Total available-for-sale securities [Member]
Estimated Fair Value, Less than 12 Months	$ 1,241	$ 4,275
Gross Unrealized Losses, Less than 12 Months	26	211
Estimated Fair Value, 12 Months or Longer	1,149	1,923
Gross Unrealized Losses, 12 Months or Longer	159	330
Estimated Fair Value, Total	2,390	6,198
Gross Unrealized Losses, Total	185	541
Corporate and other bonds [Member]
Estimated Fair Value, Less than 12 Months	600	2,552
Gross Unrealized Losses, Less than 12 Months	18	126
Estimated Fair Value, 12 Months or Longer	210	159
Gross Unrealized Losses, 12 Months or Longer	14	28
Estimated Fair Value, Total	810	2,711
Gross Unrealized Losses, Total	32	154
States, municipalities and political subdivisions [Member]
Estimated Fair Value, Less than 12 Months	84	67
Gross Unrealized Losses, Less than 12 Months	1	1
Estimated Fair Value, 12 Months or Longer	227	721
Gross Unrealized Losses, 12 Months or Longer	52	135
Estimated Fair Value, Total	311	788
Gross Unrealized Losses, Total	53	136
Residential mortgage-backed [Member]
Estimated Fair Value, Less than 12 Months	327	719
Gross Unrealized Losses, Less than 12 Months	3	36
Estimated Fair Value, 12 Months or Longer	580	874
Gross Unrealized Losses, 12 Months or Longer	78	147
Estimated Fair Value, Total	907	1,593
Gross Unrealized Losses, Total	81	183
Commercial mortgage-backed [Member]
Estimated Fair Value, Less than 12 Months	142	431
Gross Unrealized Losses, Less than 12 Months	2	39
Estimated Fair Value, 12 Months or Longer	132	169
Gross Unrealized Losses, 12 Months or Longer	15	20
Estimated Fair Value, Total	274	600
Gross Unrealized Losses, Total	17	59
Other asset-backed [Member]
Estimated Fair Value, Less than 12 Months	66	389
Gross Unrealized Losses, Less than 12 Months	1	4
Estimated Fair Value, 12 Months or Longer
Gross Unrealized Losses, 12 Months or Longer
Estimated Fair Value, Total	66	389
Gross Unrealized Losses, Total	1	4
Total asset-backed [Member]
Estimated Fair Value, Less than 12 Months	535	1,539
Gross Unrealized Losses, Less than 12 Months	6	79
Estimated Fair Value, 12 Months or Longer	712	1,043
Gross Unrealized Losses, 12 Months or Longer	93	167
Estimated Fair Value, Total	1,247	2,582
Gross Unrealized Losses, Total	99	246
US Treasury and Government [Member]
Estimated Fair Value, Less than 12 Months	22
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	22
Gross Unrealized Losses, Total	1
Total fixed maturity securities available-for-sale [Member]
Estimated Fair Value, Less than 12 Months		4,158
Gross Unrealized Losses, Less than 12 Months		206
Estimated Fair Value, 12 Months or Longer		1,923
Gross Unrealized Losses, 12 Months or Longer		330
Estimated Fair Value, Total		6,081
Gross Unrealized Losses, Total		536
Preferred stock [Member]
Estimated Fair Value, Less than 12 Months		117
Gross Unrealized Losses, Less than 12 Months		5
Estimated Fair Value, 12 Months or Longer
Gross Unrealized Losses, 12 Months or Longer
Estimated Fair Value, Total		117
Gross Unrealized Losses, Total		$ 5