Long-Term Debt and Common Stock (Details)	1 Months Ended	2 Months Ended	6 Months Ended
	Feb. 13, 2013 USD ($)	Feb. 16, 2012 USD ($)	Jun. 30, 2013 Commercial Paper [Member] USD ($)	Jun. 30, 2013 Revolving Credit Agreement [Member] USD ($)	Jun. 30, 2013 Canadian Dollar Letter of Credit Due 2014 [Member] USD ($)	Jun. 30, 2013 Canadian Dollar Letter of Credit Due 2014 [Member] CAD	Jun. 30, 2013 Floating Rate Senior Notes due 2014 [Member] USD ($)	Jun. 30, 2013 4.75% Subsidiary Debt due 2014 [Member] USD ($)
Debt Instrument Issuance [Abstract]
Short-Term Debt, Refinanced Amount							$ 350,000,000	$ 150,000,000
Debt Instrument Issuance Interest Rate								4.75%
Line of Credit Facility [Line Items]
Average Borrowings Outstanding			21,000,000
Weighted average interest rate (in hundredths)			0.31%
Line of Credit Facility, Expiration Date				Oct. 11, 2016	May 29, 2018	May 29, 2018
Restricted Cash					52,000,000	55,000,000
Maximum borrowing capacity				2,000,000,000		160,000,000
Eurodollar rate at period end (in hundredths)				1.07%
Base rate at period end (in hundredths)				3.25%
Quarterly Cash Dividends Common Stock per Share	$ 0.1875	$ 0.17