Borrowed Funds (Narrative) (Details) (USD $)	12 Months Ended
	Dec. 31, 2011 months years	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2005	Dec. 31, 2004	Mar. 31, 2011	Mar. 31, 2011 Long-Term Securities [Member] securities	Dec. 31, 2011 Repurchase Agreements [Member]	May 31, 2011 Repurchase Agreements [Member]	Dec. 31, 2010 Repurchase Agreements [Member]	Dec. 31, 2011 Minimum [Member]	Dec. 31, 2011 Maximum [Member]
Borrowed Funds [Line Items]
Securities sold under agreements to repurchase	$ 1,400,000,000	$ 1,561,000,000	$ 1,600,000,000			$ 1,500,000,000	$ 100,000,000	$ 1,400,000,000		$ 1,600,000,000
Weighted average rate of securities sold under agreements to repurchase								4.14%		4.18%
Number of long-tem securities sold							2
Weighted average interest rate							4.77%
Prepaid security sold under repurchase agreement									50,000,000
Rate of prepaid security									4.83%
Prepayment penalty security sold under agreements to repurchase									1,700,000
Total floating-to-fixed rate agreements	750,000,000
Number of floating-to-fixed rate agreements	14
Initial floating rate period on floating-to-fixed rate agreements, months, minimum	6
Initial floating rate period on floating-to-fixed rate agreements, years, maximum	1
Maximum initial floating rate, 3-month LIBOR minus 100 basis point	100
Minimum initial floating rate, 3-month LIBOR minus 340 basis point	340
Security sold under agreements to repurchase, floating-to-fix interest rates for the remainder of term											4.29%	5.07%
Total floating-to-fixed rate agreements	650,000,000
Number of fixed-to-floating securities sold under agreements to repurchase	13
Floating rate for remaining seven year term	8% minus the three-month LIBOR rate
Minimum initial fixed rate	1.00%
Maximum initial fixed rate	3.50%
Initial fixed rate period (in months)											6	18
Remainder of long-term securities, years	7
Maximum interest rate											3.25%	3.75%
Minimum interest rate	0.00%
Collateralized financing transaction at fair value	1,600,000,000	1,700,000,000
Federal home loan bank advances	225,000,000	550,000,000
Decrease in Loans from Federal Home Loan Banks	(325,000,000)
Federal home loan bank prepaid advances	450,000,000	379,400,000
Federal home loan bank prepaid advances weighted rate	$ 4.39%	$ 4.62%
Federal home loan bank prepayment penalties	18,500,000	14,300,000
Federal home loan bank weighted average interest rate	$ 2.08%	$ 4.43%
Other borrowings	880,000	8,500,000
Estimate of borrowings maturing in first quarter of 2012	880,000
Weighted average rate	0.55%	0.48%
Maximum amount of deferred bonus				225,000
Amount of deferred bonus accrued in other liabilities					610,000
Accrued interest rate per annum on deferred bonus	7.00%
Interest accrued on deferred bonus	67,000	62,000	58,000
Amount of deferred bonus	$ 995,000	$ 928,000
Basis points above prevailing interest rate	275