Intangible Assets - Summary of Intangible Assets (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount, finite-lived assets	$ 18,018	$ 18,018
Accumulated Amortization, finite-lived assets	(6,031)	(5,468)
Foreign Currency Translation Adjustment, finite-lived assets	(4)	(6)
Net Carrying Amount, finite-lived assets	11,983	12,544
Indefinite-lived Intangible Assets [Line Items]
Gross  Carrying Amount	19,265	19,265
Accumulated Amortization	(6,031)	(5,468)
Foreign Currency Translation Adjustment	(9)	(11)
Net Carrying Amount	13,225	13,786
Indefinite-lived assets - IPR&D
Indefinite-lived Intangible Assets [Line Items]
Gross Carrying Amount, indefinite-lived assets	1,247	1,247
Foreign Currency Translation Adjustment, indefinite-lived assets	(5)	(5)
Net Carrying Amount, indefinite-lived assets	1,242	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	(4,603)	(4,253)
Foreign Currency Translation Adjustment, finite-lived assets	0	0
Net Carrying Amount, finite-lived assets	6,117	6,467
Indefinite-lived Intangible Assets [Line Items]
Accumulated Amortization	(4,603)	(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	(933)	(761)
Foreign Currency Translation Adjustment, finite-lived assets	0	0
Net Carrying Amount, finite-lived assets	5,267	5,439
Indefinite-lived Intangible Assets [Line Items]
Accumulated Amortization	(933)	(761)
Other
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount, finite-lived assets	1,098	1,098
Accumulated Amortization, finite-lived assets	(495)	(454)
Foreign Currency Translation Adjustment, finite-lived assets	(4)	(6)
Net Carrying Amount, finite-lived assets	599	638
Indefinite-lived Intangible Assets [Line Items]
Accumulated Amortization	$ (495)	$ (454)