Investment in Change Healthcare Joint Venture (Details)			3 Months Ended								12 Months Ended
	Mar. 09, 2020 shares	Jul. 01, 2019 USD ($) $ / shares	Mar. 31, 2020 USD ($) $ / shares	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($) $ / shares	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2020 USD ($) $ / shares	Mar. 31, 2019 USD ($) $ / shares	Mar. 31, 2018 USD ($)	Mar. 10, 2020 $ / shares shares	Jul. 31, 2019 executive_officer	Apr. 01, 2019 USD ($)	Apr. 01, 2018 USD ($)	Mar. 31, 2017
Schedule of Equity Method Investments [Line Items]
Pre-tax gain on sale of business											$ 0	$ 0	$ 37,000,000
Cumulative effect adjustment to opening balance of retained earnings																$ 11,000,000	$ 154,000,000
Equity earnings and charges from investment in Change Healthcare Joint Venture											$ (36,000,000)	$ (43,000,000)	(32,000,000)
Shares distributed in split-off (shares) | shares	176,000,000.0
Common stock, par value (in dollars per share) | $ / shares			$ 0.01				$ 0.01				$ 0.01	$ 0.01
Carrying value of equity method investments			$ 0				$ 3,513,000,000				$ 0	$ 3,513,000,000
Tax Receivable Agreement (“TRA”)
Schedule of Equity Method Investments [Line Items]
Percentage of net cash tax savings realized or deemed realized under TRA (percent)			85.00%								85.00%
Separation of Change Healthcare JV
Schedule of Equity Method Investments [Line Items]
Shares distributed in split-off (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
Retained Earnings
Schedule of Equity Method Investments [Line Items]
Cumulative effect adjustment to opening balance of retained earnings																11,000,000	$ 154,000,000
Other | Tax Receivable Agreement (“TRA”) | Change Healthcare
Schedule of Equity Method Investments [Line Items]
Pre-tax credit representing reduction in TRA liability												90,000,000
After-tax credit representing reduction in TRA liability												66,000,000
Noncurrent liability			$ 0				0				$ 0	0
Other | Operating Segments
Schedule of Equity Method Investments [Line Items]
Pre-tax credit representing reduction in TRA liability													(46,000,000)
After-tax credit representing reduction in TRA liability													(30,000,000)
Change Healthcare
Schedule of Equity Method Investments [Line Items]
Equity earnings and charges from investment in Change Healthcare Joint Venture			$ 44,000,000	$ 28,000,000	$ 51,000,000	$ (4,000,000)	32,000,000	$ 50,000,000	$ 56,000,000	$ 56,000,000
Number of company's executive officers on joint venture's Board of Directors | executive_officer															2
Change Healthcare | Technology Solutions | Core MTS Businesses | Operating Segments
Schedule of Equity Method Investments [Line Items]
Pre-tax gain on sale of business													37,000,000
Gain from sale of business, after tax													22,000,000
Proceeds from divestiture of businesses													126,000,000
Change Healthcare, Inc.
Schedule of Equity Method Investments [Line Items]
Net cash proceeds from IPO		$ 888,000,000
Proceeds from other security offering		$ 279,000,000
Change Healthcare, Inc. | IPO
Schedule of Equity Method Investments [Line Items]
Offering price (in usd per share) | $ / shares		$ 13
Change Healthcare, Inc. | Change Healthcare
Schedule of Equity Method Investments [Line Items]
Ownership interest in Joint Venture (percent)		41.50%
Contributions made in exchange for additional membership interests		$ 609,000,000
Corporate Joint Venture
Schedule of Equity Method Investments [Line Items]
Ownership interest in Joint Venture (percent)																		70.00%
Pre-tax dilution loss					246,000,000						246,000,000
After-tax dilution loss					184,000,000						184,000,000
Carrying value of equity method investments							3,500,000,000					3,500,000,000
Excess of carrying value over proportionate share of investment net assets							$ 4,200,000,000					4,200,000,000
Corporate Joint Venture | Transition Services Agreements (“TSA”)
Schedule of Equity Method Investments [Line Items]
Total fees charged under the TSA											22,000,000	60,000,000	91,000,000
Corporate Joint Venture | Change Healthcare
Schedule of Equity Method Investments [Line Items]
Ownership interest in Joint Venture (percent)		58.50%
Pre-tax other-than-temporary impairment					1,200,000,000						1,200,000,000
After-tax other-than-temporary impairment					$ 864,000,000						864,000,000
Equity earnings and charges from investment in Change Healthcare Joint Venture											$ 119,000,000	194,000,000	248,000,000
Provisional tax benefit													$ 76,000,000
Pre-tax credit representing reduction in TRA liability									(90,000,000)			(90,000,000)
After-tax credit representing reduction in TRA liability									$ (66,000,000)			$ (66,000,000)
Corporate Joint Venture | Change Healthcare | ASU 2014-09 | Retained Earnings
Schedule of Equity Method Investments [Line Items]
Cumulative effect adjustment to opening balance of retained earnings																$ 80,000,000
Corporate Joint Venture | Change Healthcare, Inc.
Schedule of Equity Method Investments [Line Items]
Ownership interest in Joint Venture (percent)																		30.00%