Fair Value Measurements (Details) - USD ($)	3 Months Ended
	Sep. 30, 2019	Mar. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying amount of liabilities	$ 7,644,000,000	$ 7,595,000,000
Recurring | Fair value, inputs, level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying amount of liabilities	7,600,000,000	7,600,000,000
Estimated fair values of liabilities	8,300,000,000	7,900,000,000
Recurring | Fair value, inputs, level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in money market funds	199,000,000	1,205,000,000
Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities measured at fair value	0	$ 0
Joint Venture | Change Healthcare JV
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Pre-tax impairment charge	1,157,000,000
After-tax impairment charge	$ 864,000,000