Investments (Securities in a gross unrealized loss position) (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	$ 7,464	$ 2,855
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	342	70
Estimated Fair Value, 12 Months or Longer	502	707
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	50	29
Estimated Fair Value, Total	7,966	3,562
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	392	99
Corporate and other bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	4,882	1,330
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	302	46
Estimated Fair Value, 12 Months or Longer	162	277
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	40	15
Estimated Fair Value, Total	5,044	1,607
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	342	61
States, municipalities and political subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	338	335
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	8	5
Estimated Fair Value, 12 Months or Longer	75	127
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	3
Estimated Fair Value, Total	413	462
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	8	8
Residential mortgage-backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	963	293
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	9	5
Estimated Fair Value, 12 Months or Longer	164	189
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	8	8
Estimated Fair Value, Total	1,127	482
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	17	13
Commercial mortgage-backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	652	264
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	10	2
Estimated Fair Value, 12 Months or Longer	96	99
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	2	3
Estimated Fair Value, Total	748	363
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	12	5
Other asset-backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	552	607
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	8	10
Estimated Fair Value, 12 Months or Longer	5	7
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Estimated Fair Value, Total	557	614
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	8	10
Total asset-backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	2,167	1,164
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	27	17
Estimated Fair Value, 12 Months or Longer	265	295
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	10	11
Estimated Fair Value, Total	2,432	1,459
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	37	28
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	3
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	0
Estimated Fair Value, 12 Months or Longer	0	4
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Estimated Fair Value, Total	4	7
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	0	0
Foreign Government Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	54	3
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1	0
Estimated Fair Value, 12 Months or Longer	0	3
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Estimated Fair Value, Total	54	6
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	1	0
Redeemable preferred stock [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	3	3
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	0
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	3	3
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	0	0
Total fixed maturity securities available-for-sale [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	7,448	2,838
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	338	68
Estimated Fair Value, 12 Months or Longer	502	706
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	50	29
Estimated Fair Value, Total	7,950	3,544
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	388	97
Common 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	1
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	1
Preferred stock [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	13	17
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	3	2
Estimated Fair Value, 12 Months or Longer	0	1
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Estimated Fair Value, Total	13	18
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	3	$ 2
Total equity securities available-for-sale [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	16
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	4
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	16
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ 4