Investments (Impaired Mortgage Loans) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012	Dec. 31, 2011
Impaired Mortgage Loans
Unpaid Principal Balance	$ 737		$ 737			$ 750
Valuation allowances	302	361	302	361	332	347	446	481
Recorded Investment	631		631			616
Average Investment	703	484	713	515
Interest Income	6	2	10	6
Loans with a Valuation Allowance [Member]
Impaired Mortgage Loans
Unpaid Principal Balance	341		341			568
Recorded Investment	325		325			556
Valuation allowances	72		72			117
Recorded Investment	253		253			439
Loans Without Valuation Allowances [Member]
Impaired Mortgage Loans
Unpaid Principal Balance	396		396			182
Recorded Investment	378		378			177
Commercial mortgage loans portfolio segment [Member]
Impaired Mortgage Loans
Unpaid Principal Balance	555		555			548
Valuation allowances	242	300	242	300	275	293	368	398
Recorded Investment	474		474			445
Average Investment	531	258	534	283
Interest Income	4	0	7	3
Commercial mortgage loans portfolio segment [Member] | Loans with a Valuation Allowance [Member]
Impaired Mortgage Loans
Unpaid Principal Balance	241		241			445
Recorded Investment	228		228			436
Valuation allowances	56		56			94
Recorded Investment	172		172			342
Commercial mortgage loans portfolio segment [Member] | Loans Without Valuation Allowances [Member]
Impaired Mortgage Loans
Unpaid Principal Balance	314		314			103
Recorded Investment	302		302			103
Agricultural [Member]
Impaired Mortgage Loans
Unpaid Principal Balance	168		168			189
Valuation allowances	49	59	49	59	54	52	75	81
Recorded Investment	145		145			160
Average Investment	158	214	165	219
Interest Income	2	2	3	3
Agricultural [Member] | Loans with a Valuation Allowance [Member]
Impaired Mortgage Loans
Unpaid Principal Balance	87		87			110
Recorded Investment	84		84			107
Valuation allowances	14		14			21
Recorded Investment	70		70			86
Agricultural [Member] | Loans Without Valuation Allowances [Member]
Impaired Mortgage Loans
Unpaid Principal Balance	81		81			79
Recorded Investment	75		75			74
Residential [Member]
Impaired Mortgage Loans
Unpaid Principal Balance	14		14			13
Valuation allowances	11	2	11	2	3	2	3	2
Recorded Investment	12		12			11
Average Investment	14	12	14	13
Interest Income	0	0	0	0
Residential [Member] | Loans with a Valuation Allowance [Member]
Impaired Mortgage Loans
Unpaid Principal Balance	13		13			13
Recorded Investment	13		13			13
Valuation allowances	2		2			2
Recorded Investment	11		11			11
Residential [Member] | Loans Without Valuation Allowances [Member]
Impaired Mortgage Loans
Unpaid Principal Balance	1		1			0
Recorded Investment	$ 1		$ 1			$ 0