Guarantees Repurchase Requests (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015		Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Gurantees [Abstract]
Unpaid Principal Balance Of Unresolved Repurchase Requests	$ 17	[1]	$ 47	[1]	$ 126	[1]	$ 655
Unpaid Principal Balance of Repurchase Requests Received	73		158		1,511
Unpaid Principal Balance of Repurchase Requests Resolved by Repurchase	22		28		1,134
Unpaid Principal Balance of Repurchase Requests Resolved by Settlement	81		209		906
Unpaid Principal Balance of Repurchase Request Loans Resolved	$ 103		$ 237		$ 2,040

[1] Comprised of $11 million, $44 million, and $122 million from the GSEs, and $6 million, $3 million, and $4 million from non-agency investors at December 31, 2015, 2014, and 2013, respectively.