Investments (Details 13) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Carrying value of non-impaired mortgage loans, summarized by debt service coverage ratio distribution
Total mortgage loans	$ 6,570	$ 7,139
Mortgage loans, non-impaired
Carrying value of non-impaired mortgage loans, summarized by debt service coverage ratio distribution
Fixed rate mortgage loans	6,201	6,659
Variable rate mortgage loans	214	236
Total mortgage loans	6,415	6,895
Net carrying value of impaired mortgage loans
Impaired mortgage loans with a valuation allowance	147	244
Impaired loans without a valuation allowance	8
Total impaired mortgage loans	155	244
Valuation allowance on impaired mortgage loans	42	63	84
Rollforward of the valuation allowance on impaired mortgage loans
Valuation allowance on impaired mortgage loans, beginning balance	63	84	95
Net (decrease) increase in valuation allowance	(5)	37	65
Charge offs	(16)	(58)	(76)
Valuation allowance on impaired mortgage loans, ending balance	42	63	84
Carrying value of past due mortgage loans
Less than 90 days past due	21
90 days or greater past due	4	43
Total past due	25	43
Current loans	6,545	7,096
Carrying value of mortgage loans	6,570	7,139
Mortgage loans, non-impaired \| Below 1.0
Carrying value of non-impaired mortgage loans, summarized by debt service coverage ratio distribution
Fixed rate mortgage loans	267	345
Total mortgage loans	267	345
Mortgage loans, non-impaired \| 1.0 - 1.25
Carrying value of non-impaired mortgage loans, summarized by debt service coverage ratio distribution
Fixed rate mortgage loans	1,208	1,527
Variable rate mortgage loans	20	44
Total mortgage loans	1,228	1,571
Mortgage loans, non-impaired \| 1.26 - 1.50
Carrying value of non-impaired mortgage loans, summarized by debt service coverage ratio distribution
Fixed rate mortgage loans	1,458	1,573
Variable rate mortgage loans	46	24
Total mortgage loans	1,504	1,597
Mortgage loans, non-impaired \| Above 1.50
Carrying value of non-impaired mortgage loans, summarized by debt service coverage ratio distribution
Fixed rate mortgage loans	3,268	3,214
Variable rate mortgage loans	148	168
Total mortgage loans	3,416	3,382
Mortgage loans
Average carrying value and interest income recognized on impaired mortgage loans
Average impaired mortgage loans	$ 202	$ 210	$ 278

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Financing receivables that are less than 90 days past due.

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A valuation allowance for financing receivables that are expected to be uncollectible.

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Amount of direct write-downs of financing receivables charged against the allowance.

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Average amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

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