Investments (Details 7) (USD $)	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013
Investment in limited partnerships
Asset recorded	$ 979,000,000us-gaap_EquityMethodInvestments	$ 1,086,000,000us-gaap_EquityMethodInvestments
Income (loss) recognized due to valuation adjustments by the partnerships	7,000,000	(28,000,000)
Income (loss) recorded	106,000,000	189,000,000
Per the limited partner financial statements
Total partnership assets	45,000,000,000	50,000,000,000
Total partnership liabilities	4,000,000,000	5,000,000,000
Total partnership valuation adjustment gains (losses)	(1,000,000,000)	2,000,000,000
Total partnership net income	7,000,000,000	7,000,000,000
Indemnity
Investment in limited partnerships
Number of partnerships	58	61
Asset recorded	113,000,000	146,000,000
Income (loss) recognized due to valuation adjustments by the partnerships	2,000,000	(3,000,000)
Income (loss) recorded	9,000,000	25,000,000
Indemnity \| Private equity
Investment in limited partnerships
Number of partnerships	27	29
Asset recorded	52,000,000	62,000,000
Income (loss) recognized due to valuation adjustments by the partnerships	(4,000,000)	(3,000,000)
Income (loss) recorded	8,000,000	9,000,000
Indemnity \| Private equity \| Less than 10%
Investment in limited partnerships
Number of partnerships	24	26
Asset recorded	34,000,000	46,000,000
Income (loss) recognized due to valuation adjustments by the partnerships	(7,000,000)	(6,000,000)
Income (loss) recorded	7,000,000	9,000,000
Indemnity \| Private equity \| Greater than or equal to 10% but less than 50%
Investment in limited partnerships
Number of partnerships	3	3
Asset recorded	18,000,000	16,000,000
Income (loss) recognized due to valuation adjustments by the partnerships	3,000,000	3,000,000
Income (loss) recorded	1,000,000	0
Indemnity \| Private equity \| Greater than 50%
Investment in limited partnerships
Number of partnerships	0	0
Asset recorded	0	0
Income (loss) recognized due to valuation adjustments by the partnerships	0	0
Income (loss) recorded	0	0
Indemnity \| Mezzanine debt
Investment in limited partnerships
Number of partnerships	15	15
Asset recorded	14,000,000	20,000,000
Income (loss) recognized due to valuation adjustments by the partnerships	0	0
Income (loss) recorded	2,000,000	3,000,000
Indemnity \| Mezzanine debt \| Less than 10%
Investment in limited partnerships
Number of partnerships	11	11
Asset recorded	10,000,000	14,000,000
Income (loss) recognized due to valuation adjustments by the partnerships	0	0
Income (loss) recorded	2,000,000	1,000,000
Indemnity \| Mezzanine debt \| Greater than or equal to 10% but less than 50%
Investment in limited partnerships
Number of partnerships	3	3
Asset recorded	4,000,000	6,000,000
Income (loss) recognized due to valuation adjustments by the partnerships	0	0
Income (loss) recorded	0	2,000,000
Indemnity \| Mezzanine debt \| Greater than 50%
Investment in limited partnerships
Number of partnerships	1	1
Asset recorded	0	0
Income (loss) recognized due to valuation adjustments by the partnerships	0	0
Income (loss) recorded	0	0
Indemnity \| Real estate
Investment in limited partnerships
Number of partnerships	16	17
Asset recorded	47,000,000	64,000,000
Income (loss) recognized due to valuation adjustments by the partnerships	6,000,000	0
Income (loss) recorded	(1,000,000)	13,000,000
Indemnity \| Real estate \| Less than 10%
Investment in limited partnerships
Number of partnerships	11	12
Asset recorded	36,000,000	44,000,000
Income (loss) recognized due to valuation adjustments by the partnerships	5,000,000	0
Income (loss) recorded	(2,000,000)	5,000,000
Indemnity \| Real estate \| Greater than or equal to 10% but less than 50%
Investment in limited partnerships
Number of partnerships	3	3
Asset recorded	4,000,000	14,000,000
Income (loss) recognized due to valuation adjustments by the partnerships	1,000,000	(1,000,000)
Income (loss) recorded	0	4,000,000
Indemnity \| Real estate \| Greater than 50%
Investment in limited partnerships
Number of partnerships	2	2
Asset recorded	7,000,000	6,000,000
Income (loss) recognized due to valuation adjustments by the partnerships	0	1,000,000
Income (loss) recorded	1,000,000	4,000,000
Exchange
Investment in limited partnerships
Number of partnerships	102	103
Asset recorded	866,000,000	940,000,000
Income (loss) recognized due to valuation adjustments by the partnerships	5,000,000	(25,000,000)
Income (loss) recorded	97,000,000	164,000,000
Exchange \| Private equity
Investment in limited partnerships
Number of partnerships	45	47
Asset recorded	418,000,000	463,000,000
Income (loss) recognized due to valuation adjustments by the partnerships	1,000,000	(11,000,000)
Income (loss) recorded	46,000,000	81,000,000
Exchange \| Private equity \| Less than 10%
Investment in limited partnerships
Number of partnerships	42	44
Asset recorded	344,000,000	396,000,000
Income (loss) recognized due to valuation adjustments by the partnerships	(12,000,000)	(24,000,000)
Income (loss) recorded	43,000,000	79,000,000
Exchange \| Private equity \| Greater than or equal to 10% but less than 50%
Investment in limited partnerships
Number of partnerships	3	3
Asset recorded	74,000,000	67,000,000
Income (loss) recognized due to valuation adjustments by the partnerships	13,000,000	13,000,000
Income (loss) recorded	3,000,000	2,000,000
Exchange \| Private equity \| Greater than 50%
Investment in limited partnerships
Number of partnerships	0	0
Asset recorded	0	0
Income (loss) recognized due to valuation adjustments by the partnerships	0	0
Income (loss) recorded	0	0
Exchange \| Mezzanine debt
Investment in limited partnerships
Number of partnerships	28	26
Asset recorded	170,000,000	172,000,000
Income (loss) recognized due to valuation adjustments by the partnerships	(3,000,000)	(1,000,000)
Income (loss) recorded	22,000,000	23,000,000
Exchange \| Mezzanine debt \| Less than 10%
Investment in limited partnerships
Number of partnerships	21	19
Asset recorded	120,000,000	117,000,000
Income (loss) recognized due to valuation adjustments by the partnerships	0	1,000,000
Income (loss) recorded	16,000,000	13,000,000
Exchange \| Mezzanine debt \| Greater than or equal to 10% but less than 50%
Investment in limited partnerships
Number of partnerships	4	4
Asset recorded	23,000,000	23,000,000
Income (loss) recognized due to valuation adjustments by the partnerships	(3,000,000)	(3,000,000)
Income (loss) recorded	3,000,000	7,000,000
Exchange \| Mezzanine debt \| Greater than 50%
Investment in limited partnerships
Number of partnerships	3	3
Asset recorded	27,000,000	32,000,000
Income (loss) recognized due to valuation adjustments by the partnerships	0	1,000,000
Income (loss) recorded	3,000,000	3,000,000
Exchange \| Real estate
Investment in limited partnerships
Number of partnerships	29	30
Asset recorded	278,000,000	305,000,000
Income (loss) recognized due to valuation adjustments by the partnerships	7,000,000	(13,000,000)
Income (loss) recorded	29,000,000	60,000,000
Exchange \| Real estate \| Less than 10%
Investment in limited partnerships
Number of partnerships	22	22
Asset recorded	207,000,000	211,000,000
Income (loss) recognized due to valuation adjustments by the partnerships	18,000,000	(10,000,000)
Income (loss) recorded	7,000,000	34,000,000
Exchange \| Real estate \| Greater than or equal to 10% but less than 50%
Investment in limited partnerships
Number of partnerships	5	6
Asset recorded	44,000,000	71,000,000
Income (loss) recognized due to valuation adjustments by the partnerships	6,000,000	(2,000,000)
Income (loss) recorded	2,000,000	10,000,000
Exchange \| Real estate \| Greater than 50%
Investment in limited partnerships
Number of partnerships	2	2
Asset recorded	27,000,000	23,000,000
Income (loss) recognized due to valuation adjustments by the partnerships	(17,000,000)	(1,000,000)
Income (loss) recorded	$ 20,000,000	$ 16,000,000

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Total net income (loss) excluding valuation adjustments reported by all investees accounted for under the equity method. There is generally a one-quarter lag in the reporting of limited partnership investments by the reporting entity due to the timing of when financial statements are received.

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Total valuation adjustments reported in net income (loss) by all investees accounted for under the equity method. There is generally a one-quarter lag in the reporting of limited partnership investments by the reporting entity due to the timing of when financial statements are received.

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Represents the entity's proportionate share of net income (loss) excluding valuation adjustments of its investee to which the equity method of accounting is applied. There is a one-quarter lag in the reporting of limited partnership investments by the reporting entity due to the timing of when financial statements are received.

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The amount of assets reported by an equity method investment of the entity.

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