Repurchase Arrangements And Similar Borrowings, Including Related Hedging Activity (Schedule Of Swap Agreements Expiration Period And Characteristics) (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2010
Repurchase Arrangements And Similar Borrowings, Including Interest Rate Hedging Activity [Line Items]
Notional Amount	$ 6,600,000	$ 100,000
Average Fixed Rate Payment Requirement		4.09%
Average expiration	16 months
Currently-Paying Contracts [Member]
Repurchase Arrangements And Similar Borrowings, Including Interest Rate Hedging Activity [Line Items]
Notional Amount	4,200,000
Average Fixed Rate Payment Requirement	0.75%
Average expiration	9 months
Currently-Paying Contracts [Member] | First Quarter 2013 [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%
Currently-Paying Contracts [Member] | Second Quarter 2013 [Member]
Repurchase Arrangements And Similar Borrowings, Including Interest Rate Hedging Activity [Line Items]
Notional Amount	700,000
Average Fixed Rate Payment Requirement	0.96%
Currently-Paying Contracts [Member] | Third Quarter 2013 [Member]
Repurchase Arrangements And Similar Borrowings, Including Interest Rate Hedging Activity [Line Items]
Notional Amount	300,000
Average Fixed Rate Payment Requirement	0.87%
Currently-Paying Contracts [Member] | Fourth Quarter 2013 [Member]
Repurchase Arrangements And Similar Borrowings, Including Interest Rate Hedging Activity [Line Items]
Notional Amount	800,000
Average Fixed Rate Payment Requirement	0.78%
Currently-Paying Contracts [Member] | First Quarter 2014 [Member]
Repurchase Arrangements And Similar Borrowings, Including Interest Rate Hedging Activity [Line Items]
Notional Amount	200,000
Average Fixed Rate Payment Requirement	0.60%
Currently-Paying Contracts [Member] | Second Quarter 2014 [Member]
Repurchase Arrangements And Similar Borrowings, Including Interest Rate Hedging Activity [Line Items]
Notional Amount	400,000
Average Fixed Rate Payment Requirement	0.51%
Currently-Paying Contracts [Member] | Third Quarter 2014 [Member]
Repurchase Arrangements And Similar Borrowings, Including Interest Rate Hedging Activity [Line Items]
Notional Amount	200,000
Average Fixed Rate Payment Requirement	0.51%
Currently-Paying Contracts [Member] | Fourth Quarter 2014 [Member]
Repurchase Arrangements And Similar Borrowings, Including Interest Rate Hedging Activity [Line Items]
Notional Amount	500,000
Average Fixed Rate Payment Requirement	0.58%
Forward-Starting Contracts [Member]
Repurchase Arrangements And Similar Borrowings, Including Interest Rate Hedging Activity [Line Items]
Notional Amount	2,400,000
Average Fixed Rate Payment Requirement	0.47%
Average expiration	29 months
Forward-Starting Contracts [Member] | First Quarter 2015 [Member]
Repurchase Arrangements And Similar Borrowings, Including Interest Rate Hedging Activity [Line Items]
Notional Amount	1,100,000
Average Fixed Rate Payment Requirement	0.50%
Forward-Starting Contracts [Member] | Second Quarter 2015 [Member]
Repurchase Arrangements And Similar Borrowings, Including Interest Rate Hedging Activity [Line Items]
Notional Amount	200,000
Average Fixed Rate Payment Requirement	0.43%
Forward-Starting Contracts [Member] | Third Quarter 2015 [Member]
Repurchase Arrangements And Similar Borrowings, Including Interest Rate Hedging Activity [Line Items]
Notional Amount	400,000
Average Fixed Rate Payment Requirement	0.47%
Forward-Starting Contracts [Member] | Fourth Quarter 2015 [Member]
Repurchase Arrangements And Similar Borrowings, Including Interest Rate Hedging Activity [Line Items]
Notional Amount	$ 700,000
Average Fixed Rate Payment Requirement	0.43%