Derivative Financial Instruments (Summary Of Outstanding Fair Value Hedges) (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
Sep. 30, 2017	Dec. 31, 2016
Derivative [Line Items]
Contractual Notional Amount	$ 6,263.1	$ 16,834.9
Interest Rate Swaps [Member]
Derivative [Line Items]
Contractual Notional Amount	1,235.0	1,385.0
Interest Rate Swaps [Member] \| 2017 [Member] \| Interest Rate Received 4.350% [Member]
Derivative [Line Items]
Contractual Notional Amount	$ 50.0	$ 0.0
Derivative, Fixed Interest Rate	4.35%	4.35%
Investment Options, Expiration Date	Aug. 15, 2020	Aug. 15, 2020
Interest Rate Swaps [Member] \| 2015 [Member] \| Interest Rate Received 4.350% [Member]
Derivative [Line Items]
Contractual Notional Amount	$ 200.0	$ 200.0
Derivative, Fixed Interest Rate	4.35%	4.35%
Investment Options, Expiration Date	Aug. 15, 2020	Aug. 15, 2020
Interest Rate Swaps [Member] \| 2014 [Member] \| Interest Rate Received 4.350% [Member]
Derivative [Line Items]
Contractual Notional Amount	$ 150.0	$ 150.0
Derivative, Fixed Interest Rate	4.35%	4.35%
Investment Options, Expiration Date	Aug. 15, 2020	Aug. 15, 2020
Interest Rate Swaps [Member] \| 2013 [Member] \| Interest Rate Received 4.350% [Member]
Derivative [Line Items]
Contractual Notional Amount	$ 10.0	$ 10.0
Derivative, Fixed Interest Rate	4.35%	4.35%
Investment Options, Expiration Date	Aug. 15, 2020	Aug. 15, 2020
Interest Rate Swaps [Member] \| 2012 [Member] \| Interest Rate Received 4.350% [Member]
Derivative [Line Items]
Contractual Notional Amount	$ 200.0	$ 200.0
Derivative, Fixed Interest Rate	4.35%	4.35%
Investment Options, Expiration Date	Aug. 15, 2020	Aug. 15, 2020
Interest Rate Swaps [Member] \| 2012 [Member] \| Interest Rate Received 1.875% [Member]
Derivative [Line Items]
Contractual Notional Amount	$ 625.0	$ 625.0
Derivative, Fixed Interest Rate	1.875%	1.875%
Investment Options, Expiration Date	Jan. 15, 2018	Jan. 15, 2018
Interest Rate Swaps [Member] \| 2012 [Member] \| Interest Rate Received 2.375% [Member]
Derivative [Line Items]
Contractual Notional Amount	$ 0.0	$ 200.0
Derivative, Fixed Interest Rate	2.375%	2.375%
Investment Options, Expiration Date	Feb. 15, 2017	Feb. 15, 2017

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

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- Definition

Expiration date of the option.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Footnote 5

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- Definition

Fixed interest rate related to the interest rate derivative.

+ References

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- Definition

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+ References

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