Investments (Securities in a gross unrealized loss position) (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	$ 4,314	$ 7,464
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	227	342
Estimated Fair Value, 12 Months or Longer	604	502
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	60	50
Estimated Fair Value, Total	4,918	7,966
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	287	392
Corporate and other bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	2,669	4,882
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	174	302
Estimated Fair Value, 12 Months or Longer	274	162
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	50	40
Estimated Fair Value, Total	2,943	5,044
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	224	342
States, municipalities and political subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	90	338
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	3	8
Estimated Fair Value, 12 Months or Longer	64	75
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Estimated Fair Value, Total	154	413
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	3	8
Residential mortgage-backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	376	963
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	11	9
Estimated Fair Value, 12 Months or Longer	159	164
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	8	8
Estimated Fair Value, Total	535	1,127
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	19	17
Commercial mortgage-backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	505	652
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	14	10
Estimated Fair Value, 12 Months or Longer	102	96
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	2	2
Estimated Fair Value, Total	607	748
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	16	12
Other asset-backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	572	552
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	20	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	577	557
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	20	8
Total asset-backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	1,453	2,167
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	45	27
Estimated Fair Value, 12 Months or Longer	266	265
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	10	10
Estimated Fair Value, Total	1,719	2,432
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	55	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	23	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	23	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	54	54
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	54	54
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	1	1
Redeemable preferred stock [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	2	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	2	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	4,291	7,448
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	223	338
Estimated Fair Value, 12 Months or Longer	604	502
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	60	50
Estimated Fair Value, Total	4,895	7,950
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	283	388
Common stock [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value, Less than 12 Months	6	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	6	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	17	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	17	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	23	16
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	4	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	23	16
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ 4	$ 4

Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for twelve months or longer.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27290-111563

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