Long-Term Debt (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Summary of long-term debt
Long-term Debt	$ 6,444	$ 6,684
Fixed and floating rate Federal Home Loan Bank advances with maturities ranging from January 2013 to February 2016 [Member] | Senior debt [Member]
Summary of long-term debt
Long-term Debt	3,000	3,625
Floating rate notes due June 2012 [Member] | Senior debt [Member]
Summary of long-term debt
Long-term Debt		500
Floating rate notes due June 2014 [Member] | Senior debt [Member]
Summary of long-term debt
Long-term Debt	300	300
Fixed rate 2.125% notes due December 2013 [Member] | Senior debt [Member]
Summary of long-term debt
Long-term Debt	399	399
Fixed rate 3.00% notes due June 2016 [Member] | Senior debt [Member]
Summary of long-term debt
Long-term Debt	699	698
Fixed rate 2.125% notes due June 2017 [Member] | Senior debt [Member]
Summary of long-term debt
Long-term Debt	499
Fixed rate 3.50% notes due June 2022 [Member] | Senior debt [Member]
Summary of long-term debt
Long-term Debt	397
Fixed rate 6.03% notes due July 2014 (related to consolidated VIE) [Member] | Note payable [Member]
Summary of long-term debt
Long-term Debt	8	8
Fixed rate 5.25% notes due December 2013 [Member] | Subordinated debt [Member]
Summary of long-term debt
Long-term Debt	409	413
Fixed rate 5.95% notes due May 2016 [Member] | Subordinated debt [Member]
Summary of long-term debt
Long-term Debt	$ 734	$ 741