Guarantees Repurchase Requests (Additional Information) (Details) - USD ($) $ in Millions	Jun. 30, 2016		Dec. 31, 2015	Jun. 30, 2015		Dec. 31, 2014
Unpaid Principal Balance Of Unresolved Repurchase Requests	$ 10	[1]	$ 17	$ 24	[1]	$ 47
US Government Sponsored Agency [Member]
Unpaid Principal Balance Of Unresolved Repurchase Requests	6			23
Non-Government Sponsored Agency [Member]
Unpaid Principal Balance Of Unresolved Repurchase Requests	$ 4			$ 1

[1] Comprised of $6 million and $23 million from the GSEs, and $4 million and $1 million from non-agency investors at June 30, 2016 and 2015, respectively.