Intangible Assets - Summary of Intangible Assets (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Intangible Assets, Net (Excluding Goodwill) [Abstract]
Gross Carrying Amount	$ 20,751,000,000	$ 20,904,000,000
Foreign Currency Translation Adjustment	(6,000,000)
Intangible assets, net	15,738,000,000	17,100,000,000
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	18,704,000,000	18,154,000,000
Accumulated Amortization	5,007,000,000	3,804,000,000
Foreign Currency Translation Adjustment	(3,000,000)
Net Carrying Amount	13,694,000,000	14,350,000,000
Indefinite-lived Intangible Assets [Line Items]
Indefinite-lived Intangible Assets (Excluding Goodwill)	0
Indefinite-lived intangible assets - IPR&D
Indefinite-lived Intangible Assets [Line Items]
Indefinite-lived Intangible Assets (Excluding Goodwill)	2,047,000,000	2,750,000,000
Net Carrying Amount	2,044,000,000	2,750,000,000
In Process Research and Development [Member]
Indefinite-lived Intangible Assets [Line Items]
Indefinite-lived Intangible Assets, Foreign Currency Translation Gain (Loss)	(3,000,000)
Intangible asset - sofosbuvir
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	10,720,000,000	10,720,000,000
Accumulated Amortization	3,554,000,000	2,855,000,000
Foreign Currency Translation Adjustment	0
Net Carrying Amount	7,166,000,000	7,865,000,000
Intangible asset - axicabtagene ciloleucel (DLBCL)
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	6,200,000,000	6,200,000,000
Accumulated Amortization	416,000,000	72,000,000
Foreign Currency Translation Adjustment	0
Net Carrying Amount	5,784,000,000	6,128,000,000
Intangible asset - Ranexa
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	688,000,000	688,000,000
Accumulated Amortization	678,000,000	566,000,000
Foreign Currency Translation Adjustment	0
Net Carrying Amount	10,000,000	122,000,000
Other
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	1,096,000,000	546,000,000
Accumulated Amortization	359,000,000	311,000,000
Foreign Currency Translation Adjustment	(3,000,000)
Net Carrying Amount	$ 734,000,000	$ 235,000,000