Investments (Details 7) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2015 USD ($) Partnerships	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($) Partnerships	Sep. 30, 2014 USD ($)	Dec. 31, 2014 USD ($) Partnerships
Investments in limited partnerships
Equity in earnings of limited partnerships	$ 43	$ 34	$ 143	$ 111
Asset recorded	927		927		$ 979
Income (loss) recognized due to valuation adjustments by the partnerships			9		7
Income (loss) recorded			134		106
Per the limited partner financial statements
Total partnership assets	41,000		41,000		45,000
Total partnership liabilities	4,000		4,000		4,000
Total partnership valuation adjustment gains (losses)			500		(1,000)
Total partnership net income			5,000		$ 7,000
Indemnity
Investments in limited partnerships
Equity in earnings of limited partnerships	$ 4	4	$ 17	13
Number of partnerships | Partnerships	56		56		58
Asset recorded	$ 95		$ 95		$ 113
Income (loss) recognized due to valuation adjustments by the partnerships			(6)		2
Income (loss) recorded			$ 23		$ 9
Indemnity | Private equity
Investments in limited partnerships
Number of partnerships | Partnerships	27		27		27
Asset recorded	$ 51		$ 51		$ 52
Income (loss) recognized due to valuation adjustments by the partnerships			9		(4)
Income (loss) recorded			$ 4		$ 8
Indemnity | Private equity | Less than 10%
Investments in limited partnerships
Number of partnerships | Partnerships	24		24		24
Asset recorded	$ 23		$ 23		$ 34
Income (loss) recognized due to valuation adjustments by the partnerships			(2)		(7)
Income (loss) recorded			$ 2		$ 7
Indemnity | Private equity | Greater than or equal to 10% but less than 50%
Investments in limited partnerships
Number of partnerships | Partnerships	3		3		3
Asset recorded	$ 28		$ 28		$ 18
Income (loss) recognized due to valuation adjustments by the partnerships			11		3
Income (loss) recorded			$ 2		$ 1
Indemnity | Mezzanine debt
Investments in limited partnerships
Number of partnerships | Partnerships	14		14		15
Asset recorded	$ 13		$ 13		$ 14
Income (loss) recognized due to valuation adjustments by the partnerships			0		0
Income (loss) recorded			$ 2		$ 2
Indemnity | Mezzanine debt | Less than 10%
Investments in limited partnerships
Number of partnerships | Partnerships	10		10		11
Asset recorded	$ 8		$ 8		$ 10
Income (loss) recognized due to valuation adjustments by the partnerships			0		0
Income (loss) recorded			$ 1		$ 2
Indemnity | Mezzanine debt | Greater than or equal to 10% but less than 50%
Investments in limited partnerships
Number of partnerships | Partnerships	3		3		3
Asset recorded	$ 5		$ 5		$ 4
Income (loss) recognized due to valuation adjustments by the partnerships			0		0
Income (loss) recorded			$ 1		$ 0
Indemnity | Mezzanine debt | Greater than 50%
Investments in limited partnerships
Number of partnerships | Partnerships	1		1		1
Asset recorded	$ 0		$ 0		$ 0
Income (loss) recognized due to valuation adjustments by the partnerships			0		0
Income (loss) recorded			$ 0		$ 0
Indemnity | Real estate
Investments in limited partnerships
Number of partnerships | Partnerships	15		15		16
Asset recorded	$ 31		$ 31		$ 47
Income (loss) recognized due to valuation adjustments by the partnerships			(15)		6
Income (loss) recorded			$ 17		$ (1)
Indemnity | Real estate | Less than 10%
Investments in limited partnerships
Number of partnerships | Partnerships	11		11		11
Asset recorded	$ 21		$ 21		$ 36
Income (loss) recognized due to valuation adjustments by the partnerships			(11)		5
Income (loss) recorded			$ 11		$ (2)
Indemnity | Real estate | Greater than or equal to 10% but less than 50%
Investments in limited partnerships
Number of partnerships | Partnerships	2		2		3
Asset recorded	$ 4		$ 4		$ 4
Income (loss) recognized due to valuation adjustments by the partnerships			(6)		1
Income (loss) recorded			$ 6		$ 0
Indemnity | Real estate | Greater than 50%
Investments in limited partnerships
Number of partnerships | Partnerships	2		2		2
Asset recorded	$ 6		$ 6		$ 7
Income (loss) recognized due to valuation adjustments by the partnerships			2		0
Income (loss) recorded			0		$ 1
Exchange
Investments in limited partnerships
Equity in earnings of limited partnerships	$ 39	$ 30	$ 126	$ 98
Number of partnerships | Partnerships	107		107		102
Asset recorded	$ 832		$ 832		$ 866
Income (loss) recognized due to valuation adjustments by the partnerships			15		5
Income (loss) recorded			$ 111		$ 97
Exchange | Private equity
Investments in limited partnerships
Number of partnerships | Partnerships	46		46		45
Asset recorded	$ 418		$ 418		$ 418
Income (loss) recognized due to valuation adjustments by the partnerships			50		1
Income (loss) recorded			$ 40		$ 46
Exchange | Private equity | Less than 10%
Investments in limited partnerships
Number of partnerships | Partnerships	43		43		42
Asset recorded	$ 306		$ 306		$ 344
Income (loss) recognized due to valuation adjustments by the partnerships			5		(12)
Income (loss) recorded			$ 32		$ 43
Exchange | Private equity | Greater than or equal to 10% but less than 50%
Investments in limited partnerships
Number of partnerships | Partnerships	3		3		3
Asset recorded	$ 112		$ 112		$ 74
Income (loss) recognized due to valuation adjustments by the partnerships			45		13
Income (loss) recorded			$ 8		$ 3
Exchange | Mezzanine debt
Investments in limited partnerships
Number of partnerships | Partnerships	28		28		28
Asset recorded	$ 166		$ 166		$ 170
Income (loss) recognized due to valuation adjustments by the partnerships			(2)		(3)
Income (loss) recorded			$ 17		$ 22
Exchange | Mezzanine debt | Less than 10%
Investments in limited partnerships
Number of partnerships | Partnerships	21		21		21
Asset recorded	$ 115		$ 115		$ 120
Income (loss) recognized due to valuation adjustments by the partnerships			(4)		0
Income (loss) recorded			$ 13		$ 16
Exchange | Mezzanine debt | Greater than or equal to 10% but less than 50%
Investments in limited partnerships
Number of partnerships | Partnerships	4		4		4
Asset recorded	$ 24		$ 24		$ 23
Income (loss) recognized due to valuation adjustments by the partnerships			1		(3)
Income (loss) recorded			$ 2		$ 3
Exchange | Mezzanine debt | Greater than 50%
Investments in limited partnerships
Number of partnerships | Partnerships	3		3		3
Asset recorded	$ 27		$ 27		$ 27
Income (loss) recognized due to valuation adjustments by the partnerships			1		0
Income (loss) recorded			$ 2		$ 3
Exchange | Real estate
Investments in limited partnerships
Number of partnerships | Partnerships	33		33		29
Asset recorded	$ 248		$ 248		$ 278
Income (loss) recognized due to valuation adjustments by the partnerships			(33)		7
Income (loss) recorded			$ 54		$ 29
Exchange | Real estate | Less than 10%
Investments in limited partnerships
Number of partnerships | Partnerships	27		27		22
Asset recorded	$ 178		$ 178		$ 207
Income (loss) recognized due to valuation adjustments by the partnerships			(25)		18
Income (loss) recorded			$ 34		$ 7
Exchange | Real estate | Greater than or equal to 10% but less than 50%
Investments in limited partnerships
Number of partnerships | Partnerships	4		4		5
Asset recorded	$ 45		$ 45		$ 44
Income (loss) recognized due to valuation adjustments by the partnerships			(16)		6
Income (loss) recorded			$ 19		$ 2
Exchange | Real estate | Greater than 50%
Investments in limited partnerships
Number of partnerships | Partnerships	2		2		2
Asset recorded	$ 25		$ 25		$ 27
Income (loss) recognized due to valuation adjustments by the partnerships			8		(17)
Income (loss) recorded			$ 1		$ 20