Loans and Leases (Narrative) (Details) (USD $)	12 Months Ended
	Dec. 31, 2012 days	Dec. 31, 2011 days
Financing Receivable, Recorded Investment [Line Items]
Number of Loans and Leases Segment Categories	2
Aggregate short-duration advances	$ 3,300,000,000	$ 2,170,000,000
Non-accrual status principal interest payments past due days	60
Institutional [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Collectively Evaluated for Impairment	22,000,000	22,000,000
Loans or leases 90 days or more contractually past due		0
Loans or leases contractually past-due days	90	90
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Aggregate of debt restructurings	$ 197,000,000	$ 199,000,000
Loans or leases contractually past-due days	90	90