Segment Data - Revenues by Geographic Areas (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017	Mar. 31, 2016
Revenues from External Customers and Long-Lived Assets [Line Items]
Total Revenues	$ 2,969	$ 3,067	$ 5,892	$ 6,054
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Total Revenues	1,627	1,719	3,257	3,410
International
Revenues from External Customers and Long-Lived Assets [Line Items]
Total Revenues	$ 1,342	$ 1,349	$ 2,635	$ 2,644