Derivative Financial Instruments (Summary Of Outstanding Fair Value Hedges) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Derivative [Line Items]
Outstanding Notional Amount	$ 1,650.0	$ 1,105.0
Interest Rate Swap [Member] | 2012 [Member] | Expiration Date August 15, 2020 [Member] | Interest Rate Received 4.350% [Member]
Derivative [Line Items]
Outstanding Notional Amount	200.0	0
Interest Rate Received	4.35%
Expiration Date	Aug. 15, 2020
Interest Rate Swap [Member] | 2012 [Member] | Expiration Date February 15, 2017 [Member] | Interest Rate Received 2.375% [Member]
Derivative [Line Items]
Outstanding Notional Amount	200.0	0
Interest Rate Received	2.375%
Expiration Date	Feb. 15, 2017
Interest Rate Swap [Member] | 2012 [Member] | Expiration Date January 15, 2018 [Member] | Interest Rate Received 1.875% [Member]
Derivative [Line Items]
Outstanding Notional Amount	625.0	0
Interest Rate Received	1.875%
Expiration Date	Jan. 15, 2018
Interest Rate Swap [Member] | 2011 [Member] | Expiration Date January 15, 2016 [Member] | Interest Rate Received 5.250% [Member]
Derivative [Line Items]
Outstanding Notional Amount	200.0	200.0
Interest Rate Received	5.25%
Expiration Date	Jan. 15, 2016
Interest Rate Swap [Member] | 2010 [Member] | Expiration Date January 15, 2016 [Member] | Interest Rate Received 5.250% [Member]
Derivative [Line Items]
Outstanding Notional Amount	25.0	25.0
Interest Rate Received	5.25%
Expiration Date	Jan. 15, 2016
Interest Rate Swap [Member] | 2006 [Member] | Expiration Date August 1, 2012 [Member] | Interest Rate Received 6.800% [Member]
Derivative [Line Items]
Outstanding Notional Amount	0	240.0
Interest Rate Received		6.80%
Expiration Date	Aug. 01, 2012
Interest Rate Swap [Member] | 2006 [Member] | Expiration Date December 15, 2014 [Member] | Interest Rate Received 5.000% [Member]
Derivative [Line Items]
Outstanding Notional Amount	200.0	200.0
Interest Rate Received	5.00%
Expiration Date	Dec. 15, 2014
Interest Rate Swap [Member] | 2005 [Member] | Expiration Date August 1, 2012 [Member] | Interest Rate Received 6.800% [Member]
Derivative [Line Items]
Outstanding Notional Amount	0	240.0
Interest Rate Received		6.80%
Expiration Date	Aug. 01, 2012
Interest Rate Swap [Member] | 2005 [Member] | Expiration Date December 15, 2014 [Member] | Interest Rate Received 5.000% [Member]
Derivative [Line Items]
Outstanding Notional Amount	$ 200.0	$ 200.0
Interest Rate Received	5.00%
Expiration Date	Dec. 15, 2014