Stockholders' Equity - Narrative (Details)			1 Months Ended					3 Months Ended	8 Months Ended	10 Months Ended	12 Months Ended
	Mar. 09, 2020 shares	Jun. 30, 2019 $ / shares	Jul. 31, 2019 $ / shares	Dec. 31, 2018 USD ($) $ / shares shares	Mar. 31, 2018 USD ($) shares	Aug. 31, 2017 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 $ / shares shares	Mar. 31, 2018 USD ($) shares	Mar. 31, 2018 USD ($) shares	Mar. 31, 2020 USD ($) vote $ / shares shares	Mar. 31, 2019 USD ($) $ / shares shares	Mar. 31, 2018 USD ($) $ / shares shares	Mar. 10, 2020 $ / shares shares	May 31, 2018 USD ($)	Mar. 31, 2017 USD ($)
Dividends Payable [Line Items]
Number of votes | vote											1
Cash dividends declared per common share (in dollars per share) | $ / shares		$ 0.39	$ 0.41								$ 1.62	$ 1.51	$ 1.30
Average price paid per share (in dollars per share) | $ / shares								$ 143.66			$ 138.94	$ 130.72	$ 151.06
Shares repurchased											$ 1,934,000,000	$ 1,627,000,000	$ 1,650,000,000
Shares repurchased (in shares) | shares											13,900,000	13,500,000	10,500,000
Total authorization outstanding for repurchases of common stock					$ 1,096,000,000				$ 1,096,000,000	$ 1,096,000,000	$ 1,535,000,000	$ 3,469,000,000	$ 1,096,000,000			$ 2,746,000,000
Additional authorized															$ 4,000,000,000
Repurchase of common stock											$ 1,934,000,000	$ 1,627,000,000	1,650,000,000
Treasury stock retired (in shares) | shares	15,400,000											5,000,000.0
Retirement of common stock												$ 542,000,000
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											$ 53,000,000	$ (207,000,000)
Net foreign currency translation gains (losses)											149,000,000	(198,000,000)	609,000,000
Gains (losses) from net investment hedges											39,000,000	259,000,000	(268,000,000)
Retained Earnings
Dividends Payable [Line Items]
Retirement of common stock												472,000,000
Additional Paid-in Capital
Dividends Payable [Line Items]
Repurchase of common stock											0	(150,000,000)	36,000,000
Retirement of common stock												70,000,000
Accumulated Foreign Currency Adjustment Including Portion Attributable to Noncontrolling Interest
Dividends Payable [Line Items]
Other comprehensive income (loss) before reclassifications											(151,000,000)	(431,000,000)	804,000,000
Net foreign currency translation gains (losses)											(151,000,000)	(431,000,000)	804,000,000
Accumulated Foreign Currency Adjustment Attributable to Noncontrolling Interest
Dividends Payable [Line Items]
Net foreign currency translation gains (losses)											1,000,000	(61,000,000)	189,000,000
Accumulated Defined Benefit Plans Adjustment, Net Prior Service Including Portion Attributable to Noncontrolling Interest
Dividends Payable [Line Items]
Other comprehensive income (loss) before reclassifications											$ 2,000,000	$ (5,000,000)	$ (4,000,000)
Open Market Transactions
Dividends Payable [Line Items]
Repurchase of common stock (in shares) | shares													3,500,000
Average price paid per share (in dollars per share) | $ / shares											$ 144.68		$ 144.43
Repurchase of common stock													$ 500,000,000
Accelerated Share Repurchase
Dividends Payable [Line Items]
Average price paid per share (in dollars per share) | $ / shares				$ 117.98							$ 127.68
Shares repurchased					$ 500,000,000	$ 400,000,000	$ 250,000,000
Shares repurchased (in shares) | shares				2,100,000							4,700,000
Additional authorized				$ 250,000,000							$ 600,000,000
June 2017 Accelerated Share Repurchase
Dividends Payable [Line Items]
Shares repurchased (in shares) | shares										1,500,000
August 2017 Accelerated Share Repurchase
Dividends Payable [Line Items]
Shares repurchased (in shares) | shares									2,700,000
March 2018 ASR Program
Dividends Payable [Line Items]
Shares repurchased (in shares) | shares					2,500,000			1,000,000.0
May 2018 Share Repurchase Program
Dividends Payable [Line Items]
Average price paid per share (in dollars per share) | $ / shares												$ 132.14
Shares repurchased											$ 1,300,000,000	$ 1,400,000,000
Shares repurchased (in shares) | shares											9,200,000	10,400,000
Total authorization outstanding for repurchases of common stock															5,100,000,000
Additional authorized															$ 4,000,000,000.0
Net Investment Hedging
Dividends Payable [Line Items]
Gains (losses) recorded in other comprehensive income											$ 76,000,000	$ 53,000,000	$ (7,000,000)
Separation of Change Healthcare JV
Dividends Payable [Line Items]
Shares distributed to stockholders (shares) | shares	176,000,000.0
Number of shares converted into per share converted (shares) | shares														1
Common stock, par value (in dollars per share) | $ / shares														$ 0.001