Investments (Payables for Collateral on Investments) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Carrying Value Of Payables For Collateral On Investments [Abstract]
Collateral payable held for derivative investments	$ 2,567	$ 2,980
Securities pledged under securities lending agreements	197	200
Securities pledged under reverse repurchase agreements	280	280
Securities pledged for Treasury Asset-Backed Securities Loan Facility ('TALF')	37	173
Securities pledged for Federal Home Loan Bank of Indianapolis Securities ('FHLBI')	1,100	100
Total payables for collateral on investments	4,181	3,733
Fair Value Of Related Investments Or Collateral [Abstract]
Collateral payable held for derivative investments	2,567	2,980
Securities pledged under securities lending agreements	189	193
Securities pledged under reverse repurchase agreements	294	294
Securities pledged for Treasury Asset-Backed Securities Loan Facility ('TALF')	52	199
Securities pledged for Federal Home Loan Bank of Indianapolis Securities ('FHLBI')	1,936	142
Total payables for collateral on investments	$ 5,038	$ 3,808