Stockholders' Equity - Narrative (Details) $ / shares in Units, shares in Millions	1 Months Ended	3 Months Ended			6 Months Ended
	Jul. 31, 2019 $ / shares	Sep. 30, 2019 USD ($) vote $ / shares shares	Jun. 30, 2019 USD ($) $ / shares shares	Sep. 30, 2018 $ / shares	Sep. 30, 2019 USD ($) vote $ / shares	Sep. 30, 2018 $ / shares	May 31, 2019 USD ($)
Accelerated Share Repurchases [Line Items]
Number of votes per share of common stock permitted on proposals presented to stockholders (vote) | vote		1			1
Dividends declared per common share (in dollars per share) | $ / shares	$ 0.41	$ 0.41	$ 0.39	$ 0.39	$ 0.80	$ 0.73
Accelerated Share Repurchase
Accelerated Share Repurchases [Line Items]
Authorized repurchase amount (up to) | $							$ 600,000,000
Common stock repurchased (shares) | shares			4.7
Average price per share of shares repurchased (in usd per share) | $ / shares			$ 127.68
Authorized amount available for future repurchases | $		$ 2,000,000,000.0			$ 2,000,000,000.0
Open Market Transactions
Accelerated Share Repurchases [Line Items]
Common stock repurchased (shares) | shares		5.2	0.7
Value of shares repurchased under the ASR program | $		$ 750,000,000	$ 84,000,000
Average price per share of shares repurchased (in usd per share) | $ / shares		$ 144.28	$ 128.64