Investments (AFS securities backed by pools of residential and commercial mortgages) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Total Available For Sale Securities Backed By Pools Of Residential Mortgages At Risk [Member]
Schedule Of Available For Sale Securities Residential And Commercial Mortgage At Risk [Line Items]
Amortized Cost	$ 1,181	$ 2,023
Fair Value	980	1,553
Unrealized Loss	(201)	(470)
Total Available For Sale Securities Backed By Pools Of Commercial Mortgages At Risk [Member]
Schedule Of Available For Sale Securities Residential And Commercial Mortgage At Risk [Line Items]
Amortized Cost	236	472
Fair Value	192	344
Unrealized Loss	(44)	(128)
Total Available For Sale Securities Backed By Pools Of Residential And Commercial Mortgages At Risk [Member]
Schedule Of Available For Sale Securities Residential And Commercial Mortgage At Risk [Line Items]
Amortized Cost	1,417	2,495
Fair Value	1,172	1,897
Unrealized Loss	(245)	(598)
Available For Sale Securities Backed By Pools Of Residential Mortgages Subject To Detailed Analysis [Member]
Schedule Of Available For Sale Securities Residential And Commercial Mortgage At Risk [Line Items]
Amortized Cost	1,173	2,015
Fair Value	972	1,545
Unrealized Loss	(201)	(470)
Available For Sale Securities Backed By Pools Of Commercial Mortgages Subject To Detailed Analysis [Member]
Schedule Of Available For Sale Securities Residential And Commercial Mortgage At Risk [Line Items]
Amortized Cost	56	126
Fair Value	40	61
Unrealized Loss	(16)	(65)
Available For Sale Securities Backed By Pools Of Residential And Commercial Mortgages Subject To Detailed Analysis [Member]
Schedule Of Available For Sale Securities Residential And Commercial Mortgage At Risk [Line Items]
Amortized Cost	1,229	2,141
Fair Value	1,012	1,606
Unrealized Loss	$ (217)	$ (535)