Financial Guarantees (Narratives) (Details) (USD $) In Billions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Guarantor Obligations [Line Items]
Maximum potential exposure under guarantees recognized in our consolidated balance sheets	$ 50.6	$ 59.4
Maximum potential exposure under guarantees not recognized in our consolidated balance sheets	8.3	9.3
Maximum amount recoverable for on-balance sheet guarantees through available credit enhancements and recourse with third parties	13.3	14.1
Maximum amount recoverable for off-balance sheet guarantees through available credit enhancements and recourse with third parties	3.6	4.0
Fair value of guaranty obligation	$ 1.8	$ 2.2
Minimum [Member]
Guarantor Obligations [Line Items]
Contractual terms of our guarantees	30 days	30 days
Maximum [Member]
Guarantor Obligations [Line Items]
Contractual terms of our guarantees	40 years	40 years
Loans with higher risk characteristics (original debt service coverage ratio)	1.10	1.10
Loans with higher risk characteristics (current debt service coverage ratio)	1.0	1.0
Single-Family [Member] | Minimum [Member]
Guarantor Obligations [Line Items]
Serious delinquency, days past due	90 days	90 days
Multifamily [Member] | Minimum [Member]
Guarantor Obligations [Line Items]
Serious delinquency, days past due	60 days	60 days