Borrowings (Details 4) (USD $)	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Borrowings
Total	$ 1,100,000,000	$ 1,100,000,000
Reverse repurchase agreements
Borrowings
2017	600,000,000
2018	200,000,000
2020	300,000,000
Total	1,100,000,000	1,100,000,000	1,700,000,000
Callable within the next three months	100,000,000
Callable in 2016	100,000,000
Callable in 2017	$ 100,000,000