Debt and Credit Facilities (Narrative) (Details) (USD $)	3 Months Ended
	Mar. 31, 2013	Feb. 15, 2013	Dec. 31, 2012
Commercial Paper	$ 0		$ 0
Short-term borrowings and current maturities of long-term debt	965,100,000		963,700,000
Line of credit facility, amount outstanding	2,000,000,000
Four Year Revolving Credit Facility [Member]
Line of credit facility, amount outstanding	1,000,000,000
Line of credit facility, expiration date	May 20, 2015
Five Year Revolving Credit Facility [Member]
Line of credit facility, amount outstanding	1,000,000,000
Line of credit facility, expiration date	Mar. 15, 2017
Debentures With Put Feature [Member]
Short-term borrowings and current maturities of long-term debt	343,000,000		343,000,000
Debt instrument, maturity date range, start	Jan. 01, 2027
Debt instrument, maturity date range, end	Dec. 31, 2028
Debentures with put option available to be exercised		$ 37,200,000