Derivative Financial Instruments (Interest Rate Swap Derivative Positions Fixed-To-Floating Swaps, Forward Starting Swaps And Treasury Locks) (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2011
Treasury Lock Expiring July 06, 2011 With 5 Year Tenor [Member] | Treasury Lock [Member]
Notional	$ 350
Variable Rate Received	Five year U.S. Treasury
Fixed Rate Received	1.56%
Treasury Lock Expiring July 06, 2011 With 10 Year Tenor [Member] | Treasury Lock [Member]
Notional	300
Variable Rate Received	Ten year U.S. Treasury
Fixed Rate Received	2.96%
Fixed To Floating Swaps [Member]
Notional	1,150
Average Fixed Rate Received	3.82%
Fixed To Floating Swaps [Member] | Swap Expiring July 18, 2011 [Member]
Notional	300
Variable Rate Paid	Six month LIBOR
Fixed Rate Received	4.30%
Fixed To Floating Swaps [Member] | Swap Expiring August 3, 2012 [Member]
Notional	100
Variable Rate Paid	Federal funds rate
Fixed Rate Received	1.90%
Fixed To Floating Swaps [Member] | Swap Expiring July 18, 2013 [Member]
Notional	500
Variable Rate Paid	Federal funds rate
Fixed Rate Received	3.90%
Fixed To Floating Swaps [Member] | Swap Expiring July 22, 2013 [Member]
Notional	250
Variable Rate Paid	Federal funds rate
Fixed Rate Received	3.85%
Forward Starting Swap [Member] | Swap Expiring July 7, 2011 [Member]
Notional	950
Variable Rate Received	Three month LIBOR
Fixed Rate Received	3.92%
Treasury Lock [Member]
Notional	$ 650
Fixed Rate Received	2.21%