Investments (Details 6) (USD $)	9 Months Ended	12 Months Ended
Sep. 30, 2011	Dec. 31, 2010
Investment in limited partnerships
Asset recorded	$ 1,410,000,000	$ 1,324,000,000
Income (loss) recognized due to valuation adjustments by the partnerships	68,000,000	120,000,000
Income (loss) recorded	82,000,000	8,000,000
Per the limited partner financial statements
Total partnership assets	55,000,000,000	58,000,000,000
Total partnership liabilities	5,000,000,000	10,000,000,000
Total partnership valuation adjustment gains	4,000,000,000	4,000,000,000
Total partnership net income	3,000,000,000	3,000,000,000
Indemnity
Investment in limited partnerships
Number of partnerships	63	64
Asset recorded	223,000,000	216,000,000
Income (loss) recognized due to valuation adjustments by the partnerships	13,000,000	57,000,000
Income (loss) recorded	12,000,000	(36,000,000)
Indemnity \| Private equity
Investment in limited partnerships
Number of partnerships	29	29
Asset recorded	89,000,000	86,000,000
Income (loss) recognized due to valuation adjustments by the partnerships	6,000,000	7,000,000
Income (loss) recorded	7,000,000	7,000,000
Indemnity \| Private equity \| Less than 10%
Investment in limited partnerships
Number of partnerships	26	26
Asset recorded	80,000,000	78,000,000
Income (loss) recognized due to valuation adjustments by the partnerships	7,000,000	4,000,000
Income (loss) recorded	4,000,000	7,000,000
Indemnity \| Private equity \| Greater than or equal to 10% but less than 50%
Investment in limited partnerships
Number of partnerships	3	3
Asset recorded	9,000,000	8,000,000
Income (loss) recognized due to valuation adjustments by the partnerships	(1,000,000)	3,000,000
Income (loss) recorded	3,000,000	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	42,000,000	47,000,000
Income (loss) recognized due to valuation adjustments by the partnerships	(1,000,000)	6,000,000
Income (loss) recorded	6,000,000	1,000,000
Indemnity \| Mezzanine debt \| Less than 10%
Investment in limited partnerships
Number of partnerships	11	11
Asset recorded	26,000,000	30,000,000
Income (loss) recognized due to valuation adjustments by the partnerships	(1,000,000)	4,000,000
Income (loss) recorded	5,000,000	3,000,000
Indemnity \| Mezzanine debt \| Greater than or equal to 10% but less than 50%
Investment in limited partnerships
Number of partnerships	3	3
Asset recorded	15,000,000	15,000,000
Income (loss) recognized due to valuation adjustments by the partnerships	1,000,000	2,000,000
Income (loss) recorded	1,000,000	(2,000,000)
Indemnity \| Mezzanine debt \| Greater than 50%
Investment in limited partnerships
Number of partnerships	1	1
Asset recorded	1,000,000	2,000,000
Income (loss) recognized due to valuation adjustments by the partnerships	(1,000,000)	0
Income (loss) recorded	0	0
Indemnity \| Real estate
Investment in limited partnerships
Number of partnerships	19	20
Asset recorded	92,000,000	83,000,000
Income (loss) recognized due to valuation adjustments by the partnerships	8,000,000	44,000,000
Income (loss) recorded	(1,000,000)	(44,000,000)
Indemnity \| Real estate \| Less than 10%
Investment in limited partnerships
Number of partnerships	12	12
Asset recorded	62,000,000	59,000,000
Income (loss) recognized due to valuation adjustments by the partnerships	5,000,000	30,000,000
Income (loss) recorded	0	(31,000,000)
Indemnity \| Real estate \| Greater than or equal to 10% but less than 50%
Investment in limited partnerships
Number of partnerships	3	4
Asset recorded	19,000,000	14,000,000
Income (loss) recognized due to valuation adjustments by the partnerships	1,000,000	10,000,000
Income (loss) recorded	0	(10,000,000)
Indemnity \| Real estate \| Greater than 50%
Investment in limited partnerships
Number of partnerships	4	4
Asset recorded	11,000,000	10,000,000
Income (loss) recognized due to valuation adjustments by the partnerships	2,000,000	4,000,000
Income (loss) recorded	(1,000,000)	(3,000,000)
Exchange
Investment in limited partnerships
Number of partnerships	101	99
Asset recorded	1,187,000,000	1,108,000,000
Income (loss) recognized due to valuation adjustments by the partnerships	55,000,000	63,000,000
Income (loss) recorded	70,000,000	44,000,000
Exchange \| Private equity
Investment in limited partnerships
Number of partnerships	45	44
Asset recorded	584,000,000	555,000,000
Income (loss) recognized due to valuation adjustments by the partnerships	30,000,000	38,000,000
Income (loss) recorded	39,000,000	39,000,000
Exchange \| Private equity \| Less than 10%
Investment in limited partnerships
Number of partnerships	42	41
Asset recorded	544,000,000	517,000,000
Income (loss) recognized due to valuation adjustments by the partnerships	35,000,000	28,000,000
Income (loss) recorded	28,000,000	40,000,000
Exchange \| Private equity \| Greater than or equal to 10% but less than 50%
Investment in limited partnerships
Number of partnerships	3	3
Asset recorded	40,000,000	38,000,000
Income (loss) recognized due to valuation adjustments by the partnerships	(5,000,000)	10,000,000
Income (loss) recorded	11,000,000	0
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	(1,000,000)
Exchange \| Mezzanine debt
Investment in limited partnerships
Number of partnerships	22	20
Asset recorded	215,000,000	214,000,000
Income (loss) recognized due to valuation adjustments by the partnerships	(5,000,000)	14,000,000
Income (loss) recorded	26,000,000	13,000,000
Exchange \| Mezzanine debt \| Less than 10%
Investment in limited partnerships
Number of partnerships	16	14
Asset recorded	141,000,000	142,000,000
Income (loss) recognized due to valuation adjustments by the partnerships	(6,000,000)	12,000,000
Income (loss) recorded	18,000,000	13,000,000
Exchange \| Mezzanine debt \| Greater than or equal to 10% but less than 50%
Investment in limited partnerships
Number of partnerships	3	3
Asset recorded	30,000,000	41,000,000
Income (loss) recognized due to valuation adjustments by the partnerships	1,000,000	2,000,000
Income (loss) recorded	0	(2,000,000)
Exchange \| Mezzanine debt \| Greater than 50%
Investment in limited partnerships
Number of partnerships	3	3
Asset recorded	44,000,000	31,000,000
Income (loss) recognized due to valuation adjustments by the partnerships	0	0
Income (loss) recorded	8,000,000	2,000,000
Exchange \| Real estate
Investment in limited partnerships
Number of partnerships	34	35
Asset recorded	388,000,000	339,000,000
Income (loss) recognized due to valuation adjustments by the partnerships	30,000,000	11,000,000
Income (loss) recorded	5,000,000	(8,000,000)
Exchange \| Real estate \| Less than 10%
Investment in limited partnerships
Number of partnerships	25	25
Asset recorded	285,000,000	250,000,000
Income (loss) recognized due to valuation adjustments by the partnerships	27,000,000	(11,000,000)
Income (loss) recorded	1,000,000	10,000,000
Exchange \| Real estate \| Greater than or equal to 10% but less than 50%
Investment in limited partnerships
Number of partnerships	5	6
Asset recorded	61,000,000	52,000,000
Income (loss) recognized due to valuation adjustments by the partnerships	2,000,000	7,000,000
Income (loss) recorded	0	(7,000,000)
Exchange \| Real estate \| Greater than 50%
Investment in limited partnerships
Number of partnerships	4	4
Asset recorded	42,000,000	37,000,000
Income (loss) recognized due to valuation adjustments by the partnerships	1,000,000	15,000,000
Income (loss) recorded	$ 4,000,000	$ (11,000,000)

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