Financial Instruments and Risk Management (Narrative) (Details)	12 Months Ended
	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Jan. 31, 2013 USD ($) derivative_instrument	Mar. 31, 2012 USD ($) derivative_instrument
Derivative [Line Items]
Total exposure to floating rate interest rates	1.00%	1.00%
Number of interest rate derivatives terminated | derivative_instrument				8	2
Unrealized gains on interest-rate swap agreements	$ 0	$ 6,000,000
Gain (loss) on extinguishment of debt	(700,000)	0	$ 1,100,000
Loss written-off resulting from non-performance of counterparties	1,300,000
January 2013 Interest-Rate Swap Termination
Derivative [Line Items]
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
Gain (loss) on extinguishment of debt			$ 23,600,000
March 2012 Interest-Rate Swap Termination
Derivative [Line Items]
Notional amount related to discontinuation of interest rate fair value hedge					$ 350,000,000
Unrealized gains on interest-rate swap agreements					$ 46,100,000
Amortization of deferred hedge gains	6,000,000	4,900,000
Gain (loss) on extinguishment of debt	3,600,000
Foreign Exchange Contract
Derivative [Line Items]
Notional amounts of derivative contracts	1,275,000,000
Gain (loss) in other expense from undesignated foreign currency exchange contracts	1,500,000	3,000,000
Intercompany Loans
Derivative [Line Items]
Gain (loss) related to intercompany transactions for foreign currency change	2,200,000	$ (5,200,000)
Cash Flow Hedging | Foreign Exchange Contract
Derivative [Line Items]
Notional amounts of derivative contracts	$ 22,000,000