Guarantees Repurchase Requests (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014		Dec. 31, 2013
Guarantees [Abstract]
Unpaid Principal Balance Of Unresolved Repurchase Requests	$ 14	[1]	$ 17	[1]	$ 47	[1]	$ 126
Unpaid Principal Balance of Repurchase Requests Received	44		73		158
Unpaid Principal Balance of Repurchase Requests Resolved by Repurchase	(18)		(22)		(28)
Unpaid Principal Balance of Repurchase Requests Resolved by Settlement	(29)		(81)		(209)
Unpaid Principal Balance of Repurchase Request Loans Resolved	$ (47)		$ (103)		$ (237)
Pending Repurchase Requests from Non-Agency Investors	40.40%		32.90%		6.70%
Repurchase Requests Received from Non-Agency Investors	7.10%		7.20%		0.90%

[1] Comprised of $8 million, $11 million, and $44 million from the GSEs, and $6 million, $6 million, and $3 million from non-agency investors at December 31, 2016, 2015, and 2014 respectively.