Healthcare Technology Net Asset Exchange (Details) - USD ($) $ in Millions	3 Months Ended					12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016	Mar. 01, 2017
Schedule of Equity Method Investments [Line Items]
Carrying value of equity method investments	$ 3,728				$ 4,063	$ 3,728	$ 4,063
Corporate Joint Venture
Schedule of Equity Method Investments [Line Items]
Carrying value of equity method investments	3,728				4,063	3,728	4,063
Excess of carrying value over proportionate share of investment net assets	4,472				4,762	4,472	4,762
Core MTS Businesses | Corporate Joint Venture
Schedule of Equity Method Investments [Line Items]
Ownership interest in Joint Venture (percent)									70.00%
Core MTS Businesses | Technology Solutions | Operating Segments
Schedule of Equity Method Investments [Line Items]
Pre-tax gain on sale of business					3,947		3,947
Gain from sale of business, after tax					3,018
Carrying value of contributed business' net assets					1,132		1,132
Promissory notes received					$ 1,258		1,258
Transition Services Agreements (“TSA”) | Corporate Joint Venture
Schedule of Equity Method Investments [Line Items]
Total fees charged under the TSA						91
Change Healthcare | Tax Receivable Agreement (“TRA”)
Schedule of Equity Method Investments [Line Items]
Noncurrent liability	90					90			$ 136
Credit in operating expense						46
Change Healthcare
Schedule of Equity Method Investments [Line Items]
Loss from equity method investment in Change Healthcare	$ (23)	$ 90	$ 61	$ 120		248	$ 0	$ 0
Change Healthcare | Corporate Joint Venture
Schedule of Equity Method Investments [Line Items]
Loss from equity method investment in Change Healthcare						248
Provisional tax benefit						$ 76
Change Healthcare | Core MTS Businesses | Technology Solutions | Operating Segments
Schedule of Equity Method Investments [Line Items]
Pre-tax gain on sale of business				37
Gain from sale of business, after tax				$ 22
Proceeds from Divestiture of Businesses			$ 126