Income Taxes (Details)	3 Months Ended			9 Months Ended		12 Months Ended
	Dec. 31, 2018 USD ($)	Jun. 30, 2018 USD ($) reporting_unit	Dec. 31, 2017 USD ($)	Dec. 31, 2018 USD ($) reporting_unit	Dec. 31, 2017 USD ($)	Mar. 31, 2018 USD ($)
Segment Reporting Information [Line Items]
Income tax expense rates (percent)	18.90%		(37.70%)	19.70%	(3.50%)
Income tax expense related to continuing operations	$ 123,000,000		$ (263,000,000)	$ 245,000,000	$ (46,000,000)
Discrete tax benefit recognized	31,000,000		424,000,000	138,000,000	420,000,000
Tax benefits related to change in tax method of inventory rebates	58,000,000
Tax expense (benefit) related to impact of the 2017 Tax Act	27,000,000		(370,000,000)
Discrete tax benefit related to conclusion of certain tax audits			54,000,000
Pretax goodwill impairment charges	21,000,000		$ 0	591,000,000	$ 350,000,000
Unrecognized tax benefits	1,010,000,000			1,010,000,000
Unrecognized tax benefits that would reduce income tax expense and the effective tax rate	843,000,000			843,000,000
Increase (decrease) in unrecognized tax benefit	(17,000,000)			6,000,000
Provisional tax benefit due to re-measurement of deferred taxes						$ 1,324,000,000
Provisional tax expense for the one-time tax						$ 457,000,000
Discrete tax expense (benefit) related to accumulated earnings and profits	$ 10,000,000			(5,000,000)
European Pharmaceutical Solutions and Rexall businesses
Segment Reporting Information [Line Items]
Goodwill impairment, tax benefit				0
Pretax goodwill impairment charges				591,000,000
European Pharmaceutical Solutions
Segment Reporting Information [Line Items]
Pretax goodwill impairment charges		$ 570,000,000		$ 570,000,000
Number of reporting units | reporting_unit		2		2