Healthcare Technology Net Asset Exchange (Details) - USD ($)	3 Months Ended								12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017	Mar. 15, 2019
Schedule of Equity Method Investments [Line Items]
Pre-tax gain on sale of business									$ 0	$ 109,000,000	$ 0
Loss from equity method investment in Change Healthcare					$ (23,000,000)	$ 90,000,000	$ 61,000,000	$ 120,000,000
Carrying value of equity method investments	$ 3,513,000,000				3,728,000,000				3,513,000,000	3,728,000,000
Tax Receivable Agreement (“TRA”) | Change Healthcare
Schedule of Equity Method Investments [Line Items]
Noncurrent liability					90,000,000					90,000,000
Other | Tax Receivable Agreement (“TRA”) | Change Healthcare
Schedule of Equity Method Investments [Line Items]
Noncurrent liability	0								0
Pre-tax credit representing reduction in TRA liability									90,000,000
After-tax credit representing reduction in TRA liability									66,000,000
Other | Operating Segments
Schedule of Equity Method Investments [Line Items]
Pre-tax credit representing reduction in TRA liability										46,000,000
Core MTS Businesses | Technology Solutions | Operating Segments
Schedule of Equity Method Investments [Line Items]
Gain from sale of business, after tax											3,000,000,000
Corporate Joint Venture
Schedule of Equity Method Investments [Line Items]
Carrying value of equity method investments	3,513,000,000				3,728,000,000				3,513,000,000	3,728,000,000
Excess of carrying value over proportionate share of investment net assets	4,158,000,000				$ 4,472,000,000				4,158,000,000	4,472,000,000
Corporate Joint Venture | Transition Services Agreements (“TSA”)
Schedule of Equity Method Investments [Line Items]
Total fees charged under the TSA									60,000,000	91,000,000
Corporate Joint Venture | Core MTS Businesses
Schedule of Equity Method Investments [Line Items]
Ownership interest in Joint Venture (percent)						70.00%
Change Healthcare
Schedule of Equity Method Investments [Line Items]
Loss from equity method investment in Change Healthcare	$ 32,000,000	$ 50,000,000	$ 56,000,000	$ 56,000,000					194,000,000	248,000,000	0
Change Healthcare | Core MTS Businesses | Other | Operating Segments
Schedule of Equity Method Investments [Line Items]
Pre-tax gain on sale of business											$ 3,900,000,000
Change Healthcare | Core MTS Businesses | Technology Solutions | 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 | Corporate Joint Venture
Schedule of Equity Method Investments [Line Items]
Ownership interest in Joint Venture (percent)											70.00%
Loss from equity method investment in Change Healthcare									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
Change Healthcare, Inc. | Corporate Joint Venture
Schedule of Equity Method Investments [Line Items]
Ownership interest in Joint Venture (percent)												30.00%