Guarantees Repurchase Requests (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017		Mar. 31, 2016		Dec. 31, 2016	Dec. 31, 2015
Guarantees [Abstract]
Unpaid Principal Balance Of Unresolved Repurchase Requests	$ 6	[1]	$ 14	[1]	$ 14	$ 17
Unpaid Principal Balance of Repurchase Requests Received	10		11
Unpaid Principal Balance of Repurchase Requests Resolved by Repurchase	(4)		(5)
Unpaid Principal Balance of Repurchase Requests Resolved by Settlement	(14)		(9)
Unpaid Principal Balance of Repurchase Request Loans Resolved	$ (18)		$ (14)
Pending Repurchase Requests from Non-Agency Investors	11.50%		32.60%
Repurchase Requests Received from Non-Agency Investors	6.80%		0.00%

[1] Comprised of $5 million and $9 million from the GSEs, and $1 million and $5 million from non-agency investors at March 31, 2017 and 2016, respectively.