Investments (Allowance for Credit Losses and Recorded Investment in Commercial Mortgage and Other Loans) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011
Allowance for Credit Losses:
Ending balance: individually evaluated for impairment	$ 73		$ 149
Ending Balance: collectively evaluated for impairment	196		218
Ending Balance: loans acquired with deteriorated credit quality	0		0
Total	269		367
Recorded Investment:
Ending balance gross of reserves: individually evaluated for impairment	1,156		2,150
Ending balance gross of reserves: collectively evaluated for impairment	35,846		33,648
Ending balance gross of reserves: loans acquired with deteriorated credit quality	0		0
Total	37,002	[1]	35,798	[1]
Commercial Mortgage Loan [Member]
Allowance for Credit Losses:
Ending balance: individually evaluated for impairment	49		120
Ending Balance: collectively evaluated for impairment	160		174
Ending Balance: loans acquired with deteriorated credit quality	0		0
Total	209		294
Recorded Investment:
Ending balance gross of reserves: individually evaluated for impairment	1,011		1,903
Ending balance gross of reserves: collectively evaluated for impairment	31,103		28,316
Ending balance gross of reserves: loans acquired with deteriorated credit quality	0		0
Total	32,114	[1]	30,219	[1]
Agricultural Property Loans [Member]
Allowance for Credit Losses:
Ending balance: individually evaluated for impairment	12		11
Ending Balance: collectively evaluated for impairment	8		8
Ending Balance: loans acquired with deteriorated credit quality	0		0
Total	20		19
Recorded Investment:
Ending balance gross of reserves: individually evaluated for impairment	49		45
Ending balance gross of reserves: collectively evaluated for impairment	2,073		2,001
Ending balance gross of reserves: loans acquired with deteriorated credit quality	0		0
Total	2,122	[1]	2,046	[1]
Residential Property Loan [Member]
Allowance for Credit Losses:
Ending balance: individually evaluated for impairment	0		0
Ending Balance: collectively evaluated for impairment	11		16
Ending Balance: loans acquired with deteriorated credit quality	0		0
Total	11		16
Recorded Investment:
Ending balance gross of reserves: individually evaluated for impairment	0		0
Ending balance gross of reserves: collectively evaluated for impairment	790		1,034
Ending balance gross of reserves: loans acquired with deteriorated credit quality	0		0
Total	790	[1]	1,034	[1]
Other Collateralized Loans [Member]
Allowance for Credit Losses:
Ending balance: individually evaluated for impairment	12		18
Ending Balance: collectively evaluated for impairment	0		0
Ending Balance: loans acquired with deteriorated credit quality	0		0
Total	12		18
Recorded Investment:
Ending balance gross of reserves: individually evaluated for impairment	93		110
Ending balance gross of reserves: collectively evaluated for impairment	47		66
Ending balance gross of reserves: loans acquired with deteriorated credit quality	0		0
Total	140	[1]	176	[1]
Uncollateralized Loans [Member]
Allowance for Credit Losses:
Ending balance: individually evaluated for impairment	0		0
Ending Balance: collectively evaluated for impairment	17		20
Ending Balance: loans acquired with deteriorated credit quality	0		0
Total	17		20
Recorded Investment:
Ending balance gross of reserves: individually evaluated for impairment	3		92
Ending balance gross of reserves: collectively evaluated for impairment	1,833		2,231
Ending balance gross of reserves: loans acquired with deteriorated credit quality	0		0
Total	$ 1,836	[1]	$ 2,323	[1]

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