Long-Term Debt (Details)	3 Months Ended	9 Months Ended												9 Months Ended
	Sep. 30, 2014 USD ($)	Sep. 30, 2014 USD ($)	Sep. 30, 2013 USD ($)	Sep. 30, 2014 Canadian Dollar Letter of Credit Facility Due 2018 [Member] USD ($)	Sep. 30, 2014 Canadian Dollar Letter of Credit Facility Due 2018 [Member] CAD	Sep. 30, 2014 Uncommitted Credit Facility [Member] USD ($)	Sep. 30, 2013 Uncommitted Credit Facility [Member] USD ($)	Sep. 30, 2014 Commercial Paper [Member] USD ($)	Sep. 30, 2013 Commercial Paper [Member] USD ($)	Sep. 30, 2014 Revolving Credit Agreement [Member] USD ($)	Sep. 30, 2014 Floating Rate Senior Notes Due 2014 [Member] USD ($)	Sep. 30, 2014 4.75% Subsidiary Debt Due 2014 [Member] USD ($)	Sep. 30, 2014 2.95% Senior Notes Due 2015 [Member] USD ($)	Sep. 30, 2014 2.45% Senior Notes Due 2020 [Member] USD ($)
Debt Instrument Issuance [Abstract]
Debt Instrument Issuance Face Amount											$ 350,000,000	$ 150,000,000	$ 500,000,000	$ 500,000,000
Debt Instrument, Issuance Date														Mar. 21, 2014
Debt Instrument Issuance Interest Rate												4.75%		2.45%
Debt Instrument, Repayment Date											Feb. 03, 2014	Mar. 17, 2014
Proceeds from Issuance of Senior Long-Term Debt														496,000,000
Settlement of Foreign Currency Swap		31,573,000	0									32,000,000
Settlement of Interest Rate Swap											800,000
Line of Credit Facility [Line Items]
Letters of Credit Outstanding										0
Borrowings Outstanding						0		0		0
Short-term Debt, Average Outstanding Amount						100,000	0	16,000,000	23,000,000
Weighted average interest rate (in hundredths)						0.70%		0.25%	0.30%
Line of Credit Facility, Expiration Date				May 29, 2018	May 29, 2018					Oct. 11, 2016
Restricted Cash				152,000,000	170,000,000
Maximum borrowing capacity										2,000,000,000
Letter of Credit Facility Previous Maximum Capacity					160,000,000
Letter of Credit Facility Current Maximum Capacity					190,000,000
Eurodollar rate at period end (in hundredths)										1.03%
Base rate at period end (in hundredths)										3.25%
Dividends Payable, Amount Per Share After Increase	$ 0.1675	$ 0.1675
Quarterly Cash Dividends, Common Stock, Cash	$ 0.125