Indebtedness (Commercial Paper Narrative) (Details) (USD $)	3 Months Ended
	Jun. 30, 2014	Mar. 31, 2014
Debt Instrument [Line Items]
Short-term debt	$ 53,000,000	$ 387,866,000
Revolving credit facility [Member]
Debt Instrument [Line Items]
Revolving line of credit, maximum borrowing capacity	750,000,000
Commercial paper [Member]
Debt Instrument [Line Items]
Revolving line of credit, maximum borrowing capacity	750,000,000
Short-term debt, terms	maturities that vary, but will generally not exceed 90 days from the date of issue
Short-term debt	53,000,000	387,866,000
Short-term debt, weighted average interest rate	0.30%
Maximum [Member] | Commercial paper [Member]
Debt Instrument [Line Items]
Short term debt maturity period	90 days
3.65% Senior Notes Maturing July 2024 [Member] | Senior notes, net [Member]
Debt Instrument [Line Items]
Debt instrument, face amount	$ 300,000,000