Healthcare Technology Net Asset Exchange (Details) - USD ($)	3 Months Ended				6 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2018	Sep. 30, 2017	Mar. 31, 2018
Schedule of Equity Method Investments [Line Items]
Net income (loss) from Change Healthcare	$ (56,000,000)	$ (61,000,000)			$ (112,000,000)	$ (181,000,000)
Carrying value of investment	3,609,000,000				3,609,000,000		$ 3,728,000,000
Change Healthcare, LLC (“Change Healthcare”) | Tax Receivable Agreement (“TRA”)
Schedule of Equity Method Investments [Line Items]
Noncurrent liability	0				0		90,000,000
Other | Change Healthcare, LLC (“Change Healthcare”) | Tax Receivable Agreement (“TRA”)
Schedule of Equity Method Investments [Line Items]
Gain on derecognition of liability, pre-tax	90,000,000
Gain on derecognition of liability, after tax	66,000,000
Joint Venture | Transition Services Agreements (“TSA”)
Schedule of Equity Method Investments [Line Items]
Fees incurred or earned from TSA and Advisory agreements	$ 26,000,000	10,000,000			$ 36,000,000	47,000,000
Joint Venture | Core MTS Businesses
Schedule of Equity Method Investments [Line Items]
Expected ownership interest in the joint venture (percent)	70.00%				70.00%
Change Healthcare, LLC (“Change Healthcare”) | Core MTS Businesses | Operating Segments | Other
Schedule of Equity Method Investments [Line Items]
Gain from sale of business, pre-tax			$ 37,000,000	$ 3,947,000,000
Gain from sale of business, after tax			$ 22,000,000	$ 3,018,000,000
Proceeds from Divestiture of Businesses		126,000,000
Change Healthcare, LLC (“Change Healthcare”) | Joint Venture
Schedule of Equity Method Investments [Line Items]
Expected ownership interest in the joint venture (percent)				70.00%
Net income (loss) from Change Healthcare	$ (56,000,000)	$ (61,000,000)			$ (112,000,000)	$ (181,000,000)
Carrying value of investment	3,609,000,000				3,609,000,000		3,728,000,000
Excess of carrying value of investment over proportional share of book value	$ 4,269,000,000				$ 4,269,000,000		$ 4,472,000,000