Debt, Debt Narrative (Details) - Line of Credit [Member] - USD ($)	3 Months Ended
	Mar. 31, 2017	Dec. 31, 2016
Revolving Credit Facility [Member]
Revolving Credit Facility (Textual)
Line of credit facility, maximum borrowing capacity	$ 750,000,000
Line of credit facility, expiration date	Nov. 20, 2020
Line of credit facility, higher borrowing capacity option	$ 1,000,000,000
Line of credit facility, interest rate at period end (percent)	2.3125%	2.3125%
Letter of Credit [Member]
Revolving Credit Facility (Textual)
Line of credit facility, maximum borrowing capacity	$ 100,000,000