Investments (Securities in a gross unrealized loss position) (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	$ 1,630	$ 7,464
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	29	342
Estimated Fair Value, 12 Months or Longer	672	502
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	36	50
Estimated Fair Value, Total	2,302	7,966
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	65	392
Corporate and other bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	617	4,882
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	10	302
Estimated Fair Value, 12 Months or Longer	338	162
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	26	40
Estimated Fair Value, Total	955	5,044
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	36	342
States, municipalities and political subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	163	338
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	2	8
Estimated Fair Value, 12 Months or Longer	9	75
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Estimated Fair Value, Total	172	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	273	963
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	6	9
Estimated Fair Value, 12 Months or Longer	212	164
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	9	8
Estimated Fair Value, Total	485	1,127
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	15	17
Commercial mortgage-backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	391	652
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	7	10
Estimated Fair Value, 12 Months or Longer	96	96
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	1	2
Estimated Fair Value, Total	487	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	153	552
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1	8
Estimated Fair Value, 12 Months or Longer	17	5
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Estimated Fair Value, Total	170	557
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	1	8
Total asset-backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	817	2,167
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	14	27
Estimated Fair Value, 12 Months or Longer	325	265
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	10	10
Estimated Fair Value, Total	1,142	2,432
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	24	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	2	4
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	2	4
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	16	54
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	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	16	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	1,615	7,448
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	26	338
Estimated Fair Value, 12 Months or Longer	672	502
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	36	50
Estimated Fair Value, Total	2,287	7,950
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	62	388
Common stock [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	0	3
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1	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	0	3
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	1	1
Preferred stock [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	15	13
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	2	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	15	13
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	2	3
Total equity securities available-for-sale [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	15	16
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	3	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	15	16
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ 3	$ 4