Investments (Securities in a gross unrealized loss position) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	$ 2,855	$ 9,256
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	70	388
Estimated Fair Value, 12 Months or Longer	707	544
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	29	144
Estimated Fair Value, Total	3,562	9,800
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	99	532
Corporate and other bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	1,330	3,592
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	46	129
Estimated Fair Value, 12 Months or Longer	277	72
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	15	6
Estimated Fair Value, Total	1,607	3,664
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	61	135
States, municipalities and political subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	335	3,251
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	5	197
Estimated Fair Value, 12 Months or Longer	127	129
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	3	75
Estimated Fair Value, Total	462	3,380
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	8	272
Residential mortgage-backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	293	1,293
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	5	29
Estimated Fair Value, 12 Months or Longer	189	343
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	8	63
Estimated Fair Value, Total	482	1,636
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	13	92
Commercial mortgage-backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	264	640
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	2	22
Estimated Fair Value, 12 Months or Longer	99	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	3	0
Estimated Fair Value, Total	363	640
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	5	22
Other asset-backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	607	269
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	10	3
Estimated Fair Value, 12 Months or Longer	7	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Estimated Fair Value, Total	614	269
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	10	3
Total asset-backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	1,164	2,202
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	17	54
Estimated Fair Value, 12 Months or Longer	295	343
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	11	63
Estimated Fair Value, Total	1,459	2,545
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	28	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	3	13
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	1
Estimated Fair Value, 12 Months or Longer	4	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Estimated Fair Value, Total	7	13
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	0	1
Foreign Government Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	3	111
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	3
Estimated Fair Value, 12 Months or Longer	3	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Estimated Fair Value, Total	6	111
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	0	3
Redeemable preferred stock [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	3
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0
Estimated Fair Value, 12 Months or Longer	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0
Estimated Fair Value, Total	3
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	0
Total fixed maturity securities available-for-sale [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	2,838	9,169
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	68	384
Estimated Fair Value, 12 Months or Longer	706	544
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	29	144
Estimated Fair Value, Total	3,544	9,713
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	97	528
Preferred stock [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	17	87
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	2	4
Estimated Fair Value, 12 Months or Longer	1	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Estimated Fair Value, Total	18	87
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ 2	$ 4