Investments (Securities in a gross unrealized loss position) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	$ 4,903	$ 9,256
Gross Unrealized Losses, Less than 12 Months	133	388
Estimated Fair Value, 12 Months or Longer	801	544
Gross Unrealized Losses, 12 Months or Longer	135	144
Estimated Fair Value, Total	5,704	9,800
Gross Unrealized Losses, Total	268	532
Corporate and other bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	2,002	3,592
Gross Unrealized Losses, Less than 12 Months	48	129
Estimated Fair Value, 12 Months or Longer	109	72
Gross Unrealized Losses, 12 Months or Longer	8	6
Estimated Fair Value, Total	2,111	3,664
Gross Unrealized Losses, Total	56	135
States, municipalities and political subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	1,397	3,251
Gross Unrealized Losses, Less than 12 Months	56	197
Estimated Fair Value, 12 Months or Longer	244	129
Gross Unrealized Losses, 12 Months or Longer	73	75
Estimated Fair Value, Total	1,641	3,380
Gross Unrealized Losses, Total	129	272
Residential mortgage-backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	739	1,293
Gross Unrealized Losses, Less than 12 Months	13	29
Estimated Fair Value, 12 Months or Longer	347	343
Gross Unrealized Losses, 12 Months or Longer	53	63
Estimated Fair Value, Total	1,086	1,636
Gross Unrealized Losses, Total	66	92
Commercial mortgage-backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	515	640
Gross Unrealized Losses, Less than 12 Months	12	22
Estimated Fair Value, 12 Months or Longer	91
Gross Unrealized Losses, 12 Months or Longer	1
Estimated Fair Value, Total	606	640
Gross Unrealized Losses, Total	13	22
Other asset-backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	167	269
Gross Unrealized Losses, Less than 12 Months	2	3
Estimated Fair Value, 12 Months or Longer	3
Gross Unrealized Losses, 12 Months or Longer
Estimated Fair Value, Total	170	269
Gross Unrealized Losses, Total	2	3
Total asset-backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	1,421	2,202
Gross Unrealized Losses, Less than 12 Months	27	54
Estimated Fair Value, 12 Months or Longer	441	343
Gross Unrealized Losses, 12 Months or Longer	54	63
Estimated Fair Value, Total	1,862	2,545
Gross Unrealized Losses, Total	81	117
U.S. Treasury and obligations of government-sponsored enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	6	13
Gross Unrealized Losses, Less than 12 Months	1	1
Estimated Fair Value, 12 Months or Longer	3
Gross Unrealized Losses, 12 Months or Longer
Estimated Fair Value, Total	9	13
Gross Unrealized Losses, Total	1	1
Foreign Government [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	61	111
Gross Unrealized Losses, Less than 12 Months	1	3
Estimated Fair Value, 12 Months or Longer	4
Gross Unrealized Losses, 12 Months or Longer
Estimated Fair Value, Total	65	111
Gross Unrealized Losses, Total	1	3
Total fixed maturity securities available-for-sale [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	4,887	9,169
Gross Unrealized Losses, Less than 12 Months	133	384
Estimated Fair Value, 12 Months or Longer	801	544
Gross Unrealized Losses, 12 Months or Longer	135	144
Estimated Fair Value, Total	5,688	9,713
Gross Unrealized Losses, Total	268	528
Preferred stock [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	16	87
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	16	87
Gross Unrealized Losses, Total		$ 4