Investments (Details 37) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Average investment and the related interest income in impaired mortgage loans held-for-investment
Average Investment	$ 484	$ 579	$ 515	$ 560
Interest Income Recognized - Cash Basis	0	0	4	5
Interest Income Recognized - Accrual Basis	2	1	2	2
Commercial mortgage loans portfolio segment [Member]
Average investment and the related interest income in impaired mortgage loans held-for-investment
Average Investment	258	292	283	264
Interest Income Recognized - Cash Basis	0	0	3	3
Interest Income Recognized - Accrual Basis	0	0	0	1
Agricultural mortgage loans portfolio segment [Member]
Average investment and the related interest income in impaired mortgage loans held-for-investment
Average Investment	214	255	219	268
Interest Income Recognized - Cash Basis	0	0	1	2
Interest Income Recognized - Accrual Basis	2	1	2	1
Residential mortgage loans portfolio segment [Member]
Average investment and the related interest income in impaired mortgage loans held-for-investment
Average Investment	12	32	13	28
Interest Income Recognized - Cash Basis	0	0	0	0
Interest Income Recognized - Accrual Basis	$ 0	$ 0	$ 0	$ 0