Debt - Credit Facility (Narrative) (Detail) - USD ($) $ in Billions	3 Months Ended
	Jun. 30, 2017	Sep. 30, 2017
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Credit Facility, Current Borrowing Capacity		$ 2
Five Year Portion [Member]
Line of Credit Facility [Line Items]
Credit Facility, Current Borrowing Capacity		1
Credit Facility, Maturity Date	Jun. 28, 2022
One Year Plus One Year Term Out Portion [Member]
Line of Credit Facility [Line Items]
Credit Facility, Current Borrowing Capacity		$ 1
Credit Facility, Maturity Date	Jun. 27, 2019