Repurchase Arrangements And Similar Borrowings, Including Related Hedging Activity (Schedule Of Swap Agreements Expiration Period And Characteristics) (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2010
Repurchase Arrangements And Similar Borrowings, Including Interest Rate Hedging Activity [Line Items]
Notional Amount	$ 3,700,000	$ 100,000
Average Fixed Rate Payment Requirement	0.80%	4.09%
Forward-Starting Contracts [Member]
Repurchase Arrangements And Similar Borrowings, Including Interest Rate Hedging Activity [Line Items]
Notional Amount	5,100,000
Third Quarter 2012 [Member] | Currently-Paying Contracts [Member]
Repurchase Arrangements And Similar Borrowings, Including Interest Rate Hedging Activity [Line Items]
Notional Amount	200,000
Average Fixed Rate Payment Requirement	0.83%
First Quarter 2013 [Member] | Currently-Paying Contracts [Member]
Repurchase Arrangements And Similar Borrowings, Including Interest Rate Hedging Activity [Line Items]
Notional Amount	1,100,000
Average Fixed Rate Payment Requirement	0.81%
Second Quarter 2013 [Member] | Currently-Paying Contracts [Member]
Repurchase Arrangements And Similar Borrowings, Including Interest Rate Hedging Activity [Line Items]
Notional Amount	700,000
Average Fixed Rate Payment Requirement	0.96%
Third Quarter 2013 [Member] | Currently-Paying Contracts [Member]
Repurchase Arrangements And Similar Borrowings, Including Interest Rate Hedging Activity [Line Items]
Notional Amount	300,000
Average Fixed Rate Payment Requirement	0.87%
Fourth Quarter 2013 [Member] | Currently-Paying Contracts [Member]
Repurchase Arrangements And Similar Borrowings, Including Interest Rate Hedging Activity [Line Items]
Notional Amount	800,000
Average Fixed Rate Payment Requirement	0.78%
First Quarter 2014 [Member] | Currently-Paying Contracts [Member]
Repurchase Arrangements And Similar Borrowings, Including Interest Rate Hedging Activity [Line Items]
Notional Amount	200,000
Average Fixed Rate Payment Requirement	0.60%
Second Quarter 2014 [Member] | Currently-Paying Contracts [Member]
Repurchase Arrangements And Similar Borrowings, Including Interest Rate Hedging Activity [Line Items]
Notional Amount	400,000
Average Fixed Rate Payment Requirement	0.51%
Third Quarter 2014 [Member] | Forward-Starting Contracts [Member]
Repurchase Arrangements And Similar Borrowings, Including Interest Rate Hedging Activity [Line Items]
Notional Amount	200,000
Average Fixed Rate Payment Requirement	0.51%
Fourth Quarter 2014 [Member] | Forward-Starting Contracts [Member]
Repurchase Arrangements And Similar Borrowings, Including Interest Rate Hedging Activity [Line Items]
Notional Amount	500,000
Average Fixed Rate Payment Requirement	0.58%
First quarter 2015 [Member] | Forward-Starting Contracts [Member]
Repurchase Arrangements And Similar Borrowings, Including Interest Rate Hedging Activity [Line Items]
Notional Amount	$ 700,000
Average Fixed Rate Payment Requirement	0.53%