Intangible Assets - Summary of Finite-Lived Intangible Assets (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 18,154	$ 18,154
Accumulated Amortization	(4,105)	(3,804)
Foreign Currency Translation Adjustment	4
Total	14,053	14,350
Intangible asset - sofosbuvir
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	10,720	10,720
Accumulated Amortization	(3,030)	(2,855)
Foreign Currency Translation Adjustment	0
Total	7,690	7,865
Intangible asset - axicabtagene ciloleucel (DLBCL)
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	6,200	6,200
Accumulated Amortization	(158)	(72)
Foreign Currency Translation Adjustment	0
Total	6,042	6,128
Intangible asset - Ranexa
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	688	688
Accumulated Amortization	(594)	(566)
Foreign Currency Translation Adjustment	0
Total	94	122
Other
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	546	546
Accumulated Amortization	(323)	(311)
Foreign Currency Translation Adjustment	4
Total	$ 227	$ 235