Guarantees Repurchase Requests (Additional Information) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014		Dec. 31, 2014	Dec. 31, 2013
Unpaid Principal Balance of Repurchase Requests Resolved by Repurchase	$ 5		$ 6
Unpaid Principal Balance Of Unresolved Repurchase Requests	48	[1]	155	[1]	47	126
Unpaid Principal Balance of Repurchase Requests Received	20		70
Unpaid Principal Balance of Repurchase Requests Resolved by Settlement	14		35
Unpaid Principal Balance of Repurchase Request Loans Resolved	19		41
Pending Repurchase Requests from Non-Agency Investors	5.20%		1.80%
Repurchase Requests Received from Non-Agency Investors	0.00%		0.60%
US Government Sponsored Agency [Member]
Unpaid Principal Balance Of Unresolved Repurchase Requests	45		152
Non-Government Sponsored Agency [Member]
Unpaid Principal Balance Of Unresolved Repurchase Requests	$ 3		$ 3

[1] 1 Comprised of $45 million and $152 million from the GSEs, and $3 million from non-agency investors at both March 31, 2015 and 2014, respectively.