Long-Term Debt and Credit Facilities - Debt Issuances (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2017	Sep. 30, 2017
Five Year Notes at 2.25 Percent
Schedule of U.S. dollar and Euro denominated notes [Line Items]
Face amount	$ 400
Notes, term	5 years
Fixed interest rate	2.25%
Thirty Year Notes at 3.70 Percent
Schedule of U.S. dollar and Euro denominated notes [Line Items]
Face amount		$ 500
Notes, term		30 years
Fixed interest rate		3.70%