Intangible Assets - Summary of Intangible Assets (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount, finite-lived assets	$ 18,123	$ 18,018
Accumulated Amortization, finite-lived assets	(6,312)	(5,468)
Foreign Currency Translation Adjustment, finite-lived assets	(2)	(6)
Net Carrying Amount, finite-lived assets	11,809	12,544
Indefinite-lived Intangible Assets [Line Items]
Gross  Carrying Amount	19,253	19,265
Accumulated Amortization	(6,312)	(5,468)
Foreign Currency Translation Adjustment	(2)	(11)
Net Carrying Amount	12,939	13,786
Indefinite-lived assets - IPR&D
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount, indefinite-lived assets	1,130	1,247
Foreign Currency Translation Adjustment, indefinite-lived assets	0	(5)
Net Carrying Amount, indefinite-lived assets	1,130	1,242
Intangible asset - sofosbuvir
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount, finite-lived assets	10,720	10,720
Accumulated Amortization, finite-lived assets	(4,777)	(4,253)
Foreign Currency Translation Adjustment, finite-lived assets	0	0
Net Carrying Amount, finite-lived assets	5,943	6,467
Indefinite-lived Intangible Assets [Line Items]
Accumulated Amortization	(4,777)	(4,253)
Intangible asset - axicabtagene ciloleucel
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount, finite-lived assets	6,200	6,200
Accumulated Amortization, finite-lived assets	(1,019)	(761)
Foreign Currency Translation Adjustment, finite-lived assets	0	0
Net Carrying Amount, finite-lived assets	5,181	5,439
Indefinite-lived Intangible Assets [Line Items]
Accumulated Amortization	(1,019)	(761)
Other
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount, finite-lived assets	1,203	1,098
Accumulated Amortization, finite-lived assets	(516)	(454)
Foreign Currency Translation Adjustment, finite-lived assets	(2)	(6)
Net Carrying Amount, finite-lived assets	685	638
Indefinite-lived Intangible Assets [Line Items]
Accumulated Amortization	$ (516)	$ (454)