Financial Instruments and Risk Management (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Jan. 31, 2013	Mar. 31, 2012
Total exposure to floating rate interest rates	1.00%	2.00%
Unrealized gains on interest-rate swap agreements	$ 10,900,000	$ 58,100,000
Gain (loss) on extinguishment of debt	1,100,000	(5,500,000)	$ 0
Hedge loss reclassified to interest expense	136,600,000	120,500,000	$ 108,800,000
Loss written-off resulting from non-performance of counterparties	600,000
Accelerated deferred loss - treasury lock agreements	2,600,000
Foreign Exchange Contract [Member]
Notional amounts of derivative contracts	125,000,000
Gain (Loss) in other expense from undesignated foreign currency exchange contracts	(13,500,000)	(2,700,000)
2007 Lock Agreement [Member]
Notional amounts of derivative contracts	500,000,000
Hedge loss reclassified to interest expense	38,000,000
2007 Lock Agreement [Member] | 2013 Notes [Member]
Principal amount of debt	250,000,000
2007 Lock Agreement [Member] | 2018 Notes [Member]
Principal amount of debt	250,000,000
Intercompany Loans [Member]
Gain (Loss) related to intercompany transactions for foreign currency change	10,400,000	(2,500,000)
Losses Amortized to Interest Expense in Five Years [Member] | 2007 Lock Agreement [Member]
Hedge loss reclassified to interest expense	19,200,000
Losses Amortized to Interest Expense in Ten Years [Member] | 2007 Lock Agreement [Member]
Hedge loss reclassified to interest expense	18,800,000
January 2013 Interest-Rate Swap Termination [Member]
Notional Amount Related to Discontinuation of Interest Rate Fair Value Hedge				$ 1,000,000,000
Unrealized gains on interest-rate swap agreements	0			$ 90,400,000
Amortization of Deferred Hedge Gains	35,400,000	14,600,000
Gain (loss) on extinguishment of debt	23,600,000
March 2012 Interest-Rate Swap Termination [Member]
Notional Amount Related to Discontinuation of Interest Rate Fair Value Hedge					$ 350,000,000
Unrealized gains on interest-rate swap agreements	10,900,000				$ 46,100,000
Amortization of Deferred Hedge Gains	11,900,000	$ 6,600,000
Gain (loss) on extinguishment of debt	$ 5,800,000.0