Fair Value (Narrative) (Details) (USD $)	3 Months Ended				6 Months Ended
	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Mar. 31, 2011	Dec. 31, 2011
Derivatives, Fair Value [Line Items]
Fair value of AFS securities	$ 3,223,086,000	$ 3,230,795,000			$ 3,230,795,000
Percentage of bank issuers are public companies	30.00%
Probability of default, number of basis points for years 1 through 5			30
Probability of default, increase to number of base points for each year from year 2 to 5		48
Deferring collateral rate by a calibration adjustment, number of basis points					65
Weighted average assumed loss rate on deferring collateral	26.00%	26.00%			26.00%
Current interest deferral period without causing default, years	5
Net gains on sale of OREO properties	(7,832,000)			(19,750,000)
Carrying value of OREO properties	158,592,000	153,178,000			153,178,000
Highest Quality/Most Over-Collateralized Insurance-Only Tranches Discount Rate [Member]
Derivatives, Fair Value [Line Items]
Valuations for bank and insurance tranches utilized a discount rate range of LIBOR	3.75%
Lowest Credit Quality Tranche Discount Rate [Member]
Derivatives, Fair Value [Line Items]
Valuations for bank and insurance tranches utilized a discount rate range of LIBOR	33.90%
AAA [Member]
Derivatives, Fair Value [Line Items]
Percentage of difference between rated bonds	6.00%
BBB [Member]
Derivatives, Fair Value [Line Items]
Percentage of difference between rated bonds	26.00%
A-Rated Bonds [Member]
Derivatives, Fair Value [Line Items]
Percentage of difference between rated bonds	14.00%
OREO Properties [Member]
Derivatives, Fair Value [Line Items]
Net gains on sale of OREO properties	2,800,000			5,400,000
Carrying value of OREO properties	35,200,000			72,200,000
Impairment of OREO properties	700,000			4,900,000
Minimum [Member]
Derivatives, Fair Value [Line Items]
Probability of default, minimum number of basis points for year six			65
Discount rate range of LIBOR	11.70%
Minimum [Member] | Highest Quality/Most Over-Collateralized Insurance-Only Tranches Discount Rate [Member]
Derivatives, Fair Value [Line Items]
Valuations for bank and insurance tranches utilized a discount rate range of LIBOR	6.30%
Maximum [Member]
Derivatives, Fair Value [Line Items]
Discount rate range of LIBOR	66.20%
Best [Member]
Derivatives, Fair Value [Line Items]
Percentage of resulting five-year PDs	2.18%
Worst [Member]
Derivatives, Fair Value [Line Items]
Percentage of resulting five-year PDs	100.00%
First Priority Original AAA-Rated Bonds Discount Rate [Member] | Minimum [Member]
Derivatives, Fair Value [Line Items]
Discount rate range of LIBOR utilized for fair value purposes	6.30%
First Priority Original AAA-Rated Bonds Discount Rate [Member] | Maximum [Member]
Derivatives, Fair Value [Line Items]
Discount rate range of LIBOR utilized for fair value purposes	7.30%
First Priority Original AAA-Rated Bonds Discount Rate [Member] | Average [Member]
Derivatives, Fair Value [Line Items]
Discount rate average of LIBOR utilized for fair value purposes	6.50%
Lower Priority Original AAA-Rated Bonds Discount Rate [Member] | Minimum [Member]
Derivatives, Fair Value [Line Items]
Discount rate range of LIBOR utilized for fair value purposes	6.30%
Lower Priority Original AAA-Rated Bonds Discount Rate [Member] | Maximum [Member]
Derivatives, Fair Value [Line Items]
Discount rate range of LIBOR utilized for fair value purposes	8.30%
Lower Priority Original AAA-Rated Bonds Discount Rate [Member] | Average [Member]
Derivatives, Fair Value [Line Items]
Discount rate average of LIBOR utilized for fair value purposes	6.80%
Original A-Rated Bonds Discount Rate [Member] | Minimum [Member]
Derivatives, Fair Value [Line Items]
Discount rate range of LIBOR utilized for fair value purposes	6.70%
Original A-Rated Bonds Discount Rate [Member] | Maximum [Member]
Derivatives, Fair Value [Line Items]
Discount rate range of LIBOR utilized for fair value purposes	30.20%
Original A-Rated Bonds Discount Rate [Member] | Average [Member]
Derivatives, Fair Value [Line Items]
Discount rate average of LIBOR utilized for fair value purposes	15.70%
Original BBB-Rated Bonds Discount Rate [Member] | Minimum [Member]
Derivatives, Fair Value [Line Items]
Discount rate range of LIBOR utilized for fair value purposes	13.90%
Original BBB-Rated Bonds Discount Rate [Member] | Maximum [Member]
Derivatives, Fair Value [Line Items]
Discount rate range of LIBOR utilized for fair value purposes	33.90%
Original BBB-Rated Bonds Discount Rate [Member] | Average [Member]
Derivatives, Fair Value [Line Items]
Discount rate average of LIBOR utilized for fair value purposes	28.60%
Level 1 [Member]
Derivatives, Fair Value [Line Items]
Fair value of AFS securities	178,386,000	159,932,000			159,932,000
Level 2 [Member]
Derivatives, Fair Value [Line Items]
Fair value of AFS securities	1,994,526,000	1,991,915,000			1,991,915,000
Level 2 [Member] | AFS securities [Member]
Derivatives, Fair Value [Line Items]
Fair value of AFS securities	2,000,000,000
Level 3 [Member]
Derivatives, Fair Value [Line Items]
Fair value of AFS securities	1,050,174,000	1,078,948,000			1,078,948,000
Level 3 [Member] | Municipal Securities [Member]
Derivatives, Fair Value [Line Items]
Fair value of AFS securities	17,000,000
Level 3 [Member] | AFS securities [Member]
Derivatives, Fair Value [Line Items]
Fair value of AFS securities	1,100,000,000
Level 3 [Member] | Other (Including ABS CDOs) [Member]
Derivatives, Fair Value [Line Items]
Fair value of AFS securities	31,000,000
Third Party Pricing Service [Member] | Level 2 [Member]
Derivatives, Fair Value [Line Items]
Fair value of AFS securities	1,900,000,000
Third Party Pricing Service [Member] | Level 3 [Member]
Derivatives, Fair Value [Line Items]
Fair value of AFS securities	88,000,000
Licensed Internal Third Party [Member] | Level 3 [Member]
Derivatives, Fair Value [Line Items]
Fair value of AFS securities	914,000,000
Market Corroborative Data [Member] | Level 2 [Member]
Derivatives, Fair Value [Line Items]
Fair value of AFS securities	5,000,000
Market Corroborative Data [Member] | Level 2 [Member] | FAMC Securities [Member]
Derivatives, Fair Value [Line Items]
Fair value of AFS securities	$ 139,000,000