Long-Term Debt (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Debt Instrument Issuance [Abstract]
Settlement of Foreign Currency Swap			$ 31,573,000	$ 0
Line of Credit Facility [Line Items]
Dividends Payable, Amount Per Share After Increase	$ 0.1675		$ 0.1675
Quarterly Cash Dividends, Common Stock, Cash	0.125	0.09375
Uncommitted Credit Facility [Member]
Line of Credit Facility [Line Items]
Average Borrowings Outstanding	0		0
Short-term Debt, Average Outstanding Amount			200,000	0
Weighted average interest rate (in hundredths)			0.70%
Commercial Paper [Member]
Line of Credit Facility [Line Items]
Average Borrowings Outstanding	0		0
Short-term Debt, Average Outstanding Amount			18,000,000	21,000,000
Weighted average interest rate (in hundredths)			0.25%	0.31%
Revolving Credit Agreement [Member]
Line of Credit Facility [Line Items]
Letters of Credit Outstanding	0		0
Average Borrowings Outstanding	0		0
Line of Credit Facility, Expiration Date			Oct. 11, 2016
Maximum borrowing capacity	2,000,000,000		2,000,000,000
Eurodollar rate at period end (in hundredths)	1.03%		1.03%
Base rate at period end (in hundredths)	3.25%		3.25%
Canadian Dollar Letter of Credit Facility Due 2018 (CAD) [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Expiration Date			May 29, 2018
Restricted Cash	170,000,000		170,000,000
Letter of Credit Facility Previous Maximum Capacity	160,000,000		160,000,000
Letter of Credit Facility Current Maximum Capacity	190,000,000		190,000,000
Canadian Dollar Letter of Credit Facility Due 2018 (USD) [Member]
Line of Credit Facility [Line Items]
Restricted Cash	159,000,000		159,000,000
Floating Rate Senior Notes Due 2014 [Member]
Debt Instrument Issuance [Abstract]
Debt Instrument Issuance Face Amount	350,000,000		350,000,000
Settlement of Interest Rate Swap			800,000
4.75% Subsidiary Debt Due 2014 [Member]
Debt Instrument Issuance [Abstract]
Debt Instrument Issuance Face Amount	150,000,000		150,000,000
Debt Instrument Issuance Interest Rate	4.75%		4.75%
Settlement of Foreign Currency Swap			32,000,000
2.45% Senior Notes Due 2020 [Member]
Debt Instrument Issuance [Abstract]
Debt Instrument Issuance Face Amount	500,000,000		500,000,000
Debt Instrument Issuance Interest Rate	2.45%		2.45%
Proceeds from Issuance of Senior Long-Term Debt			$ 496,000,000