Investment in Change Healthcare Joint Venture (Details) - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Mar. 31, 2020	Apr. 01, 2019	Mar. 31, 2019
Schedule of Equity Method Investments [Line Items]
Cumulative-effect adjustment to beginning retained earnings	$ 5,653	$ 8,068	$ 5,309		$ 8,287
Equity and earnings from investment in Change Healthcare	$ 0	4
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%
Change Healthcare JV | Joint Venture
Schedule of Equity Method Investments [Line Items]
Equity and earnings from investment in Change Healthcare		4
Retained Earnings
Schedule of Equity Method Investments [Line Items]
Cumulative-effect adjustment to beginning retained earnings	$ 13,384	$ 12,770	13,022		12,409
Opening retained earnings adjustment: adoption of new accounting standard
Schedule of Equity Method Investments [Line Items]
Cumulative-effect adjustment to beginning retained earnings			(13)		11
Opening retained earnings adjustment: adoption of new accounting standard | Retained Earnings
Schedule of Equity Method Investments [Line Items]
Cumulative-effect adjustment to beginning retained earnings			$ (13)		$ 11
Opening retained earnings adjustment: adoption of new accounting standard | ASU 2014-09 | Retained Earnings | Change Healthcare JV | Joint Venture
Schedule of Equity Method Investments [Line Items]
Cumulative-effect adjustment to beginning retained earnings				$ 80