Stockholders' Equity (Deficit) - Narrative (Details) $ / shares in Units, $ in Millions			1 Months Ended		3 Months Ended			6 Months Ended
	Jul. 23, 2021 $ / shares	Jul. 22, 2021 $ / shares	Aug. 31, 2021 shares	May 31, 2021 USD ($) $ / shares shares	Sep. 30, 2021 USD ($) vote $ / shares shares	Sep. 30, 2020 USD ($) $ / shares shares	Jun. 30, 2020 shares	Sep. 30, 2021 USD ($) vote $ / shares	Sep. 30, 2020 USD ($) $ / shares	Mar. 31, 2021 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	$ 0.47	$ 0.42			$ 0.47	$ 0.42		$ 0.89	$ 0.83
Shares repurchased					$ 280	$ 269		$ 1,280	$ 269
Authorized amount available for future repurchases					1,500			1,500
Other accrued liabilities					$ 4,429			4,429		$ 3,987
Accelerated Share Repurchase
Accelerated Share Repurchases [Line Items]
Shares repurchased				$ 1,000
Share repurchases (in shares) | shares				5,200,000
Average price of shares repurchased (in usd per share) | $ / shares				$ 193.22
Initial share settlement (in shares) | shares				4,300,000
Additional share (in shares) | shares			900,000
Common stock repurchased (in shares) | shares							0
Open Market Share Repurchase Transactions
Accelerated Share Repurchases [Line Items]
Average price of shares repurchased (in usd per share) | $ / shares					$ 203.20	$ 151.23
Common stock repurchased (in shares) | shares					1,400,000	1,800,000
Shares repurchased					$ 280	$ 269
Other accrued liabilities					$ 16	$ 21		$ 16	$ 21