Investments (Details 37) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Average investment and the related interest income in impaired mortgage loans held-for-investment
Average Investment	$ 598	$ 576	$ 557	$ 592
Interest Income Recognized - Cash Basis	2	1	6	4
Interest Income Recognized - Accrual Basis	1	0	3	1
Commercial mortgage loans portfolio segment [Member]
Average investment and the related interest income in impaired mortgage loans held-for-investment
Average Investment	395	330	334	308
Interest Income Recognized - Cash Basis	1	0	4	1
Interest Income Recognized - Accrual Basis	0	0	0	0
Agricultural mortgage loans portfolio segment [Member]
Average investment and the related interest income in impaired mortgage loans held-for-investment
Average Investment	191	229	210	258
Interest Income Recognized - Cash Basis	1	1	2	3
Interest Income Recognized - Accrual Basis	1	0	3	1
Residential mortgage loans portfolio segment [Member]
Average investment and the related interest income in impaired mortgage loans held-for-investment
Average Investment	12	17	13	26
Interest Income Recognized - Cash Basis	0	0	0	0
Interest Income Recognized - Accrual Basis	$ 0	$ 0	$ 0	$ 0