Segment Data - Revenues by Geographic Areas (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Revenues from External Customers and Long-Lived Assets [Line Items]
Total Revenues	$ 4,222	$ 2,969	$ 7,302	$ 5,892
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Total Revenues	2,325	1,627	3,982	3,257
International
Revenues from External Customers and Long-Lived Assets [Line Items]
Total Revenues	$ 1,898	$ 1,342	$ 3,321	$ 2,635