Long-Term Debt (Details) (USD $)	1 Months Ended	2 Months Ended	3 Months Ended
	Feb. 13, 2013	Feb. 16, 2012	Mar. 31, 2013
Debt Instrument Issuance [Abstract]
Debt Instrument Issuance Interest Rate			4.75%
Line of Credit Facility [Line Items]
Line of Credit Facility, Expiration Date			Oct. 11, 2016
Eurodollar rate at period end (in hundredths)			1.08%
Base rate at period end (in hundredths)			3.25%
Quarterly Cash Dividends Common Stock per Share	$ 0.1875	$ 0.17
Commercial Paper [Member]
Line of Credit Facility [Line Items]
Average Borrowings Outstanding			2,000,000
Weighted average interest rate (in hundredths)			0.36%
Revolving Credit Agreement [Member]
Line of Credit Facility [Line Items]
Maximum borrowing capacity			2,000,000,000
Floating Rate Senior Notes due 2014 [Member]
Debt Instrument Issuance [Abstract]
Debt Instrument Issuance Face Amount			350,000,000
4.75% Subsidiary Debt due 2014 [Member]
Debt Instrument Issuance [Abstract]
Debt Instrument Issuance Face Amount			150,000,000