Intangible Assets - Summary of Intangible Assets (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Intangible Assets, Net (Excluding Goodwill) [Abstract]
Gross Carrying Amount	$ 20,753	$ 20,751
Foreign Currency Translation Adjustment	(9)	(6)
Intangible assets, net	15,438	15,738
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	18,706	18,704
Accumulated Amortization	5,306	5,007
Foreign Currency Translation Adjustment	(4)	(3)
Net Carrying Amount	13,396	13,694
Indefinite-lived assets - In Process Research & Development
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount	2,047	2,047
Net Carrying Amount	2,042	2,044
In Process Research and Development [Member]
Indefinite-lived Intangible Assets [Line Items]
Indefinite-lived Intangible Assets, Foreign Currency Translation Gain (Loss)	(5)	(3)
Intangible asset - sofosbuvir
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	10,720	10,720
Accumulated Amortization	3,729	3,554
Foreign Currency Translation Adjustment	0	0
Net Carrying Amount	6,991	7,166
Intangible asset - axicabtagene ciloleucel (DLBCL)
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	6,200	6,200
Accumulated Amortization	502	416
Foreign Currency Translation Adjustment	0	0
Net Carrying Amount	5,698	5,784
Intangible asset - Ranexa
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	688	688
Accumulated Amortization	688	678
Foreign Currency Translation Adjustment	0	0
Net Carrying Amount	0	10
Other
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	1,098	1,096
Accumulated Amortization	387	359
Foreign Currency Translation Adjustment	(4)	(3)
Net Carrying Amount	$ 707	$ 734