Investments (Securities in a gross unrealized loss position) (Details) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	$ 2,120	$ 7,464
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	70	342
Estimated Fair Value, 12 Months or Longer	934	502
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	63	50
Estimated Fair Value, Total	3,054	7,966
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	133	392
Corporate and other bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	1,032	4,882
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	43	302
Estimated Fair Value, 12 Months or Longer	562	162
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	50	40
Estimated Fair Value, Total	1,594	5,044
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	93	342
States, municipalities and political subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	68	338
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	2	8
Estimated Fair Value, 12 Months or Longer	10	75
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Estimated Fair Value, Total	78	413
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	2	8
Residential mortgage-backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	293	963
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	8	9
Estimated Fair Value, 12 Months or Longer	234	164
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	12	8
Estimated Fair Value, Total	527	1,127
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	20	17
Commercial mortgage-backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	386	652
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	7	10
Estimated Fair Value, 12 Months or Longer	118	96
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	1	2
Estimated Fair Value, Total	504	748
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	8	12
Other asset-backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	306	552
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	5	8
Estimated Fair Value, 12 Months or Longer	5	5
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Estimated Fair Value, Total	311	557
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	5	8
Total asset-backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	985	2,167
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	20	27
Estimated Fair Value, 12 Months or Longer	357	265
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	13	10
Estimated Fair Value, Total	1,342	2,432
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	33	37
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		4
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		4
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss		0
Foreign Government Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	8	54
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	1
Estimated Fair Value, 12 Months or Longer	5	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Estimated Fair Value, Total	13	54
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	0	1
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	2,093	7,448
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	65	338
Estimated Fair Value, 12 Months or Longer	934	502
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	63	50
Estimated Fair Value, Total	3,027	7,950
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	128	388
Common stock [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	4	3
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	2	1
Estimated Fair Value, 12 Months or Longer	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Estimated Fair Value, Total	4	3
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	2	1
Preferred stock [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	23	13
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	3	3
Estimated Fair Value, 12 Months or Longer	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Estimated Fair Value, Total	23	13
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	3	3
Total equity securities available-for-sale [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	27	16
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	5	4
Estimated Fair Value, 12 Months or Longer	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Estimated Fair Value, Total	27	16
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ 5	$ 4