Healthcare Technology Net Asset Exchange (Details) - USD ($)	3 Months Ended						9 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Mar. 31, 2018
Schedule of Equity Method Investments [Line Items]
Gain from sale of business, pre-tax	$ 0		$ 109,000,000				$ 0	$ 109,000,000
Net income (loss) from Change Healthcare	(50,000,000)		(90,000,000)				(162,000,000)	(271,000,000)
Carrying value of investment	3,566,000,000						3,566,000,000		$ 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
Operating Segments | Other
Schedule of Equity Method Investments [Line Items]
Gain on derecognition of liability, pre-tax			(46,000,000)					(46,000,000)
Gain on derecognition of liability, after tax			(30,000,000)					(30,000,000)
Joint Venture | Transition Services Agreements (“TSA”)
Schedule of Equity Method Investments [Line Items]
Fees incurred or earned from TSA and Advisory agreements	$ 12,000,000		22,000,000				$ 48,000,000	69,000,000
Joint Venture | Core MTS Businesses
Schedule of Equity Method Investments [Line Items]
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	$ 3,900,000,000
Gain from sale of business, after tax					$ 22,000,000	$ 3,000,000,000
Proceeds from Divestiture of Businesses				$ 126,000,000
Change Healthcare, LLC (“Change Healthcare”) | Joint Venture
Schedule of Equity Method Investments [Line Items]
Ownership interest in the joint venture (percent)						70.00%
Net income (loss) from Change Healthcare	$ (50,000,000)		$ (90,000,000)				$ (162,000,000)	$ (271,000,000)
Carrying value of investment	3,566,000,000						3,566,000,000		3,728,000,000
Excess of carrying value of investment over proportional share of book value	$ 4,226,000,000						4,226,000,000		$ 4,472,000,000
Gain on derecognition of liability, pre-tax							90,000,000
Gain on derecognition of liability, after tax							$ 66,000,000