Stockholders' Equity - Narrative (Details) $ / shares in Units, $ in Millions		1 Months Ended	3 Months Ended	12 Months Ended
	Mar. 09, 2020 shares	Jul. 31, 2020 $ / shares	Jun. 30, 2020 $ / shares	Mar. 31, 2021 USD ($) vote $ / shares	Mar. 31, 2020 USD ($) $ / shares	Mar. 31, 2019 USD ($) $ / shares shares	Jan. 31, 2021 USD ($)	Mar. 10, 2020 $ / shares shares	May 31, 2018 USD ($)	Mar. 31, 2018 USD ($)
Dividends Payable [Line Items]
Number of votes | vote				1
Cash dividends declared per common share (in dollars per share) | $ / shares		$ 0.42	$ 0.41	$ 1.67	$ 1.62	$ 1.51
Total authorization outstanding for repurchases of common stock				$ 2,785	$ 1,535	$ 3,469				$ 1,096
Additional authorized							$ 2,000		$ 4,000
Treasury stock retired (in shares) | shares						5,000,000.0
Retirement of common stock						$ 542
Shares distributed to stockholders (shares) | shares	176,000,000.0
Common stock, par value (in dollars per share) | $ / shares				$ 0.01	$ 0.01
Other comprehensive income (loss) before reclassifications				$ 99	$ 53
Net foreign currency translation gains (losses)				170	149	(198)
Gains (losses) from net investment hedges				(118)	39	259
Change Healthcare
Dividends Payable [Line Items]
Shares repurchased (in shares) | shares	15,400,000
Other accrued liabilities
Dividends Payable [Line Items]
Accrued shares repurchased				8
Retained Earnings
Dividends Payable [Line Items]
Retirement of common stock						472
Additional Paid-in Capital
Dividends Payable [Line Items]
Retirement of common stock						70
Accumulated Foreign Currency Adjustment Including Portion Attributable to Noncontrolling Interest
Dividends Payable [Line Items]
Other comprehensive income (loss) before reclassifications				312	(151)	(431)
Net foreign currency translation gains (losses)				359	(151)	(431)
Accumulated Foreign Currency Adjustment Attributable to Noncontrolling Interest
Dividends Payable [Line Items]
Net foreign currency translation gains (losses)				(60)	1	(61)
Accumulated Defined Benefit Plans Adjustment, Net Prior Service Including Portion Attributable to Noncontrolling Interest
Dividends Payable [Line Items]
Other comprehensive income (loss) before reclassifications				8	2	(5)
Net Investment Hedging
Dividends Payable [Line Items]
Gains (losses) recorded in other comprehensive income				$ (119)	$ 76	$ 53
Separation of Change Healthcare JV
Dividends Payable [Line Items]
Shares distributed to stockholders (shares) | shares	176,000,000.0
Shares of common stock exchanged (shares) | shares	15,400,000
Number of shares converted into per share converted (shares) | shares								1
Common stock, par value (in dollars per share) | $ / shares								$ 0.001