Investment in Change Healthcare Joint Venture (Details) - USD ($)		3 Months Ended		9 Months Ended
	Jul. 01, 2019	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2020	Sep. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Apr. 01, 2019	Mar. 31, 2019
Schedule of Equity Method Investments [Line Items]
Shareholders' equity		$ 6,385,000,000	$ 6,692,000,000	$ 6,385,000,000	$ (277,000,000)	$ 6,090,000,000	$ 5,309,000,000			$ 8,287,000,000
Change Healthcare, Inc.
Schedule of Equity Method Investments [Line Items]
Proceeds from Issuance Initial Public Offering	$ 888,000,000
Proceeds from concurrent offering of other securities	$ 279,000,000
Change Healthcare, Inc. | IPO
Schedule of Equity Method Investments [Line Items]
Offering price (in usd per share)	$ 13
Transition Services Agreements (“TSA”)
Schedule of Equity Method Investments [Line Items]
Fees earned from TSA				18,000,000
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%
Receivable recognized					$ 0
Joint Venture
Schedule of Equity Method Investments [Line Items]
Ownership interest (percent)								70.00%
Change Healthcare JV | Change Healthcare, Inc.
Schedule of Equity Method Investments [Line Items]
Contributions made in exchange for additional membership interests	$ 609,000,000
Ownership interest (percent)	41.50%
Change Healthcare JV | Joint Venture
Schedule of Equity Method Investments [Line Items]
Ownership interest (percent)	58.50%
Pre-tax dilution loss			246,000,000	246,000,000
Impairment			1,200,000,000	1,200,000,000
Proportionate loss from investment in Change Healthcare		28,000,000		75,000,000
Retained Earnings
Schedule of Equity Method Investments [Line Items]
Shareholders' equity		$ 12,075,000,000	$ 11,965,000,000	$ 12,075,000,000	$ 7,595,000,000	$ 13,890,000,000	13,022,000,000			12,409,000,000
Opening retained earnings adjustment: adoption of new accounting standard
Schedule of Equity Method Investments [Line Items]
Shareholders' equity							(13,000,000)			11,000,000
Opening retained earnings adjustment: adoption of new accounting standard | Retained Earnings
Schedule of Equity Method Investments [Line Items]
Shareholders' equity							$ (13,000,000)			$ 11,000,000
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]
Shareholders' equity									$ 80,000,000