Investments (Securities in a gross unrealized loss position) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Corporate and other bonds [Member]
Estimated Fair Value, Less than 12 Months	$ 846	$ 2,552
Gross Unrealized Losses, Less than 12 Months	13	126
Estimated Fair Value, 12 Months or Longer	108	159
Gross Unrealized Losses, 12 Months or Longer	8	28
Estimated Fair Value, Total	954	2,711
Gross Unrealized Losses, Total	21	154
States, municipalities and political subdivisions [Member]
Estimated Fair Value, Less than 12 Months	254	67
Gross Unrealized Losses, Less than 12 Months	5	1
Estimated Fair Value, 12 Months or Longer	165	721
Gross Unrealized Losses, 12 Months or Longer	39	135
Estimated Fair Value, Total	419	788
Gross Unrealized Losses, Total	44	136
Residential mortgage-backed [Member]
Estimated Fair Value, Less than 12 Months	583	719
Gross Unrealized Losses, Less than 12 Months	5	36
Estimated Fair Value, 12 Months or Longer	452	874
Gross Unrealized Losses, 12 Months or Longer	66	147
Estimated Fair Value, Total	1,035	1,593
Gross Unrealized Losses, Total	71	183
Commercial mortgage-backed [Member]
Estimated Fair Value, Less than 12 Months	85	431
Gross Unrealized Losses, Less than 12 Months	2	39
Estimated Fair Value, 12 Months or Longer	141	169
Gross Unrealized Losses, 12 Months or Longer	15	20
Estimated Fair Value, Total	226	600
Gross Unrealized Losses, Total	17	59
Other asset-backed [Member]
Estimated Fair Value, Less than 12 Months		389
Gross Unrealized Losses, Less than 12 Months		4
Estimated Fair Value, 12 Months or Longer
Gross Unrealized Losses, 12 Months or Longer
Estimated Fair Value, Total		389
Gross Unrealized Losses, Total		4
Total asset-backed [Member]
Estimated Fair Value, Less than 12 Months	668	1,539
Gross Unrealized Losses, Less than 12 Months	7	79
Estimated Fair Value, 12 Months or Longer	593	1,043
Gross Unrealized Losses, 12 Months or Longer	81	167
Estimated Fair Value, Total	1,261	2,582
Gross Unrealized Losses, Total	88	246
U.S. Treasury and obligations of government-sponsored enterprises [Member]
Estimated Fair Value, Less than 12 Months	23
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	23
Gross Unrealized Losses, Total	1
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
Total fixed maturity securities available-for-sale [Member]
Estimated Fair Value, Less than 12 Months	1,819	4,158
Gross Unrealized Losses, Less than 12 Months	27	206
Estimated Fair Value, 12 Months or Longer	866	1,923
Gross Unrealized Losses, 12 Months or Longer	128	330
Estimated Fair Value, Total	2,685	6,081
Gross Unrealized Losses, Total	155	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
Available-for-sale Securities [Member]
Estimated Fair Value, Less than 12 Months	1,819	4,275
Gross Unrealized Losses, Less than 12 Months	27	211
Estimated Fair Value, 12 Months or Longer	866	1,923
Gross Unrealized Losses, 12 Months or Longer	128	330
Estimated Fair Value, Total	2,685	6,198
Gross Unrealized Losses, Total	$ 155	$ 541