Guarantees Repurchase Requests (Additional Information) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016		Mar. 31, 2015		Dec. 31, 2015	Dec. 31, 2014
Unpaid Principal Balance Of Unresolved Repurchase Requests	$ 14	[1]	$ 48	[1]	$ 17	$ 47
Pending Repurchase Requests from Non-Agency Investors	32.60%		5.20%
Repurchase Requests Received from Non-Agency Investors	0.00%		0.00%
US Government Sponsored Agency [Member]
Unpaid Principal Balance Of Unresolved Repurchase Requests	$ 9		$ 45
Non-Government Sponsored Agency [Member]
Unpaid Principal Balance Of Unresolved Repurchase Requests	$ 5		$ 3

[1] Comprised of $9 million and $45 million from the GSEs, and $5 million and $3 million from non-agency investors at March 31, 2016 and 2015, respectively.