Investments (Impaired Loans) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010
Recorded Investment	$ 578	[1]	$ 1,007	[1]
Unpaid Principal Balance Principal Balance	667		1,028
Related Allowance	149		300
Average Recorded Investment	779	[2]
Interest Income Recognized	13	[3]
Commercial Mortgage Loan [Member]
Recorded Investment	532	[1]	916	[1]
Unpaid Principal Balance Principal Balance	614		917
Related Allowance	120		264
Average Recorded Investment	709	[2]
Interest Income Recognized	11	[3]
Agricultural Loan [Member]
Recorded Investment	19	[1]	1	[1]
Unpaid Principal Balance Principal Balance	19		1
Related Allowance	11		0
Average Recorded Investment	15	[2]
Interest Income Recognized	0	[3]
Residential Property Loan [Member]
Recorded Investment	0	[1]	26	[1]
Unpaid Principal Balance Principal Balance	0		31
Related Allowance	0		0
Average Recorded Investment	5	[2]
Interest Income Recognized	0	[3]
Other Collateralized Loans [Member]
Recorded Investment	21	[1]	29	[1]
Unpaid Principal Balance Principal Balance	21		29
Related Allowance	18		20
Average Recorded Investment	31	[2]
Interest Income Recognized	2	[3]
Uncollateralized Loans [Member]
Recorded Investment	6	[1]	35	[1]
Unpaid Principal Balance Principal Balance	13		50
Related Allowance	0		16
Average Recorded Investment	19	[2]
Interest Income Recognized	0	[3]
Impaired Financing Receivable with No Related Allowance [Member]
Recorded Investment	25	[1]	65	[1]
Unpaid Principal Balance Principal Balance	114		77
Related Allowance	0		0
Average Recorded Investment	42	[2]
Interest Income Recognized	1	[3]
Impaired Financing Receivable with No Related Allowance [Member] | Commercial Loan On Industrial Properties [Member]
Recorded Investment	0	[1]	0	[1]
Unpaid Principal Balance Principal Balance	0		0
Related Allowance	0		0
Average Recorded Investment	0	[2]
Interest Income Recognized	0	[3]
Impaired Financing Receivable with No Related Allowance [Member] | Commercial Loan on Retail [Member]
Recorded Investment	0	[1]	0	[1]
Unpaid Principal Balance Principal Balance	0		0
Related Allowance	0		0
Average Recorded Investment	0	[2]
Interest Income Recognized	0	[3]
Impaired Financing Receivable with No Related Allowance [Member] | Commercial Loan on Office [Member]
Recorded Investment	2	[1]	0	[1]
Unpaid Principal Balance Principal Balance	84		0
Related Allowance	0		0
Average Recorded Investment	1	[2]
Interest Income Recognized	0	[3]
Impaired Financing Receivable with No Related Allowance [Member] | Commercial Loan On Apartment And Multi Family [Member]
Recorded Investment	0	[1]	0	[1]
Unpaid Principal Balance Principal Balance	0		0
Related Allowance	0		0
Average Recorded Investment	0	[2]
Interest Income Recognized	0	[3]
Impaired Financing Receivable with No Related Allowance [Member] | Commercial Loan on Hospitality [Member]
Recorded Investment	0	[1]	64	[1]
Unpaid Principal Balance Principal Balance	0		64
Related Allowance	0		0
Average Recorded Investment	23	[2]
Interest Income Recognized	0	[3]
Impaired Financing Receivable with No Related Allowance [Member] | Commercial Loan on Other [Member]
Recorded Investment	17	[1]	0	[1]
Unpaid Principal Balance Principal Balance	17		0
Related Allowance	0		0
Average Recorded Investment	11	[2]
Interest Income Recognized	1	[3]
Impaired Financing Receivable with No Related Allowance [Member] | Commercial Mortgage Loan [Member]
Recorded Investment	19	[1]	64	[1]
Unpaid Principal Balance Principal Balance	101		64
Related Allowance	0		0
Average Recorded Investment	35	[2]
Interest Income Recognized	1	[3]
Impaired Financing Receivable with No Related Allowance [Member] | Agricultural Loan [Member]
Recorded Investment	0	[1]	1	[1]
Unpaid Principal Balance Principal Balance	0		1
Related Allowance	0		0
Average Recorded Investment	1	[2]
Interest Income Recognized	0	[3]
Impaired Financing Receivable with No Related Allowance [Member] | Residential Property Loan [Member]
Recorded Investment	0	[1]	0	[1]
Unpaid Principal Balance Principal Balance	0		0
Related Allowance	0		0
Average Recorded Investment	0	[2]
Interest Income Recognized	0	[3]
Impaired Financing Receivable with No Related Allowance [Member] | Other Collateralized Loans [Member]
Recorded Investment	0	[1]	0	[1]
Unpaid Principal Balance Principal Balance	0		0
Related Allowance	0		0
Average Recorded Investment	0	[2]
Interest Income Recognized	0	[3]
Impaired Financing Receivable with No Related Allowance [Member] | Uncollateralized Loans [Member]
Recorded Investment	6	[1]	0	[1]
Unpaid Principal Balance Principal Balance	13		12
Related Allowance	0		0
Average Recorded Investment	6	[2]
Interest Income Recognized	0	[3]
Impaired Financing Receivable with Related Allowance [Member]
Recorded Investment	553	[1]	942	[1]
Unpaid Principal Balance Principal Balance	553		951
Related Allowance	149		300
Average Recorded Investment	737	[2]
Interest Income Recognized	12	[3]
Impaired Financing Receivable with Related Allowance [Member] | Commercial Loan On Industrial Properties [Member]
Recorded Investment	54	[1]	18	[1]
Unpaid Principal Balance Principal Balance	54		18
Related Allowance	19		18
Average Recorded Investment	36	[2]
Interest Income Recognized	1	[3]
Impaired Financing Receivable with Related Allowance [Member] | Commercial Loan on Retail [Member]
Recorded Investment	89	[1]	155	[1]
Unpaid Principal Balance Principal Balance	89		155
Related Allowance	11		23
Average Recorded Investment	114	[2]
Interest Income Recognized	3	[3]
Impaired Financing Receivable with Related Allowance [Member] | Commercial Loan on Office [Member]
Recorded Investment	47	[1]	43	[1]
Unpaid Principal Balance Principal Balance	47		43
Related Allowance	3		10
Average Recorded Investment	49	[2]
Interest Income Recognized	0	[3]
Impaired Financing Receivable with Related Allowance [Member] | Commercial Loan On Apartment And Multi Family [Member]
Recorded Investment	102	[1]	323	[1]
Unpaid Principal Balance Principal Balance	102		323
Related Allowance	19		103
Average Recorded Investment	197	[2]
Interest Income Recognized	4	[3]
Impaired Financing Receivable with Related Allowance [Member] | Commercial Loan on Hospitality [Member]
Recorded Investment	129	[1]	218	[1]
Unpaid Principal Balance Principal Balance	129		218
Related Allowance	55		89
Average Recorded Investment	178	[2]
Interest Income Recognized	0	[3]
Impaired Financing Receivable with Related Allowance [Member] | Commercial Loan on Other [Member]
Recorded Investment	92	[1]	95	[1]
Unpaid Principal Balance Principal Balance	92		96
Related Allowance	13		21
Average Recorded Investment	100	[2]
Interest Income Recognized	2	[3]
Impaired Financing Receivable with Related Allowance [Member] | Commercial Mortgage Loan [Member]
Recorded Investment	513	[1]	852	[1]
Unpaid Principal Balance Principal Balance	513		853
Related Allowance	120		264
Average Recorded Investment	674	[2]
Interest Income Recognized	10	[3]
Impaired Financing Receivable with Related Allowance [Member] | Agricultural Loan [Member]
Recorded Investment	19	[1]	0	[1]
Unpaid Principal Balance Principal Balance	19		0
Related Allowance	11		0
Average Recorded Investment	14	[2]
Interest Income Recognized	0	[3]
Impaired Financing Receivable with Related Allowance [Member] | Residential Property Loan [Member]
Recorded Investment	0	[1]	26	[1]
Unpaid Principal Balance Principal Balance	0		31
Related Allowance	0		0
Average Recorded Investment	5	[2]
Interest Income Recognized	0	[3]
Impaired Financing Receivable with Related Allowance [Member] | Other Collateralized Loans [Member]
Recorded Investment	21	[1]	29	[1]
Unpaid Principal Balance Principal Balance	21		29
Related Allowance	18		20
Average Recorded Investment	31	[2]
Interest Income Recognized	2	[3]
Impaired Financing Receivable with Related Allowance [Member] | Uncollateralized Loans [Member]
Recorded Investment	0	[1]	35	[1]
Unpaid Principal Balance Principal Balance	0		38
Related Allowance	0		16
Average Recorded Investment	13	[2]
Interest Income Recognized	$ 0	[3]

[1] Recorded investment reflects the balance sheet carrying value gross of related allowance.

[2] Average recorded investment represents the average of the beginning-of-period and all subsequent quarterly end-of-period balances. The interest income recognized reflects the related year-to-date income, regardless of the impairment timing.

[3] The interest income recognized reflects the related year-to-date income, regardless of the impairment timing.