Guarantees Repurchase Requests (Additional Information) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2015		Sep. 30, 2014		Dec. 31, 2014	Dec. 31, 2013
Unpaid Principal Balance of Repurchase Requests Resolved by Repurchase	$ 17		$ 22
Unpaid Principal Balance Of Unresolved Repurchase Requests	16	[1]	45	[1]	$ 47	$ 126
Unpaid Principal Balance of Repurchase Requests Received	58		139
Unpaid Principal Balance of Repurchase Requests Resolved by Settlement	72		198
Unpaid Principal Balance of Repurchase Request Loans Resolved	$ 89		$ 220
Pending Repurchase Requests from Non-Agency Investors	6.00%		7.00%
Repurchase Requests Received from Non-Agency Investors	0.60%		0.80%
US Government Sponsored Agency [Member]
Unpaid Principal Balance Of Unresolved Repurchase Requests	$ 15		$ 42
Non-Government Sponsored Agency [Member]
Unpaid Principal Balance Of Unresolved Repurchase Requests	$ 1		$ 3

[1] 1 Comprised of $15 million and $42 million from the GSEs, and $1 million and $3 million from non-agency investors at September 30, 2015 and 2014, respectively.