Investments (Details 12) (USD $) In Millions, unless otherwise specified			3 Months Ended											3 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2013 Mortgage loans, non-impaired	Mar. 31, 2012 Mortgage loans, non-impaired	Dec. 31, 2012 Mortgage loans, non-impaired	Mar. 31, 2013 Mortgage loans, non-impaired Below 1.0	Dec. 31, 2012 Mortgage loans, non-impaired Below 1.0	Mar. 31, 2013 Mortgage loans, non-impaired 1.0 - 1.25	Dec. 31, 2012 Mortgage loans, non-impaired 1.0 - 1.25	Mar. 31, 2013 Mortgage loans, non-impaired 1.26 - 1.50	Dec. 31, 2012 Mortgage loans, non-impaired 1.26 - 1.50	Mar. 31, 2013 Mortgage loans, non-impaired Above 1.50	Dec. 31, 2012 Mortgage loans, non-impaired Above 1.50	Mar. 31, 2013 Mortgage loans	Dec. 31, 2012 Mortgage loans
Carrying value of non-impaired mortgage loans, summarized by debt service coverage ratio distribution
Fixed rate mortgage loans			$ 6,187		$ 6,201	$ 232	$ 267	$ 1,095	$ 1,208	$ 1,471	$ 1,458	$ 3,389	$ 3,268
Variable rate mortgage loans			205		214			20	20	41	46	144	148
Total mortgage loans	6,434	6,570	6,392		6,415	232	267	1,115	1,228	1,512	1,504	3,533	3,416
Net carrying value of impaired mortgage loans
Impaired mortgage loans with a valuation allowance			24		147
Impaired loans without a valuation allowance			18		8
Total impaired mortgage loans			42		155
Valuation allowance on impaired mortgage loans			15	60
Average carrying value and interest income recognized on impaired mortgage loans
Average impaired mortgage loans														99	236
Rollforward of the valuation allowance on impaired mortgage loans
Valuation allowance on impaired mortgage loans, beginning balance			42	63
Net (decrease) increase in valuation allowance			(26)	3
Charge offs			(1)	(6)
Valuation allowance on impaired mortgage loans, ending balance			15	60
Carrying value of past due mortgage loans
Less than 90 days past due			38		21
90 days or greater past due			4		4
Total past due			42		25
Current loans			6,392		6,545
Carrying value of mortgage loans			$ 6,434		$ 6,570