Intangible Assets - Summary of Finite Lived Intangible Assets (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 11,863	$ 11,863
Accumulated Amortization	2,678	2,048
Intangible asset - sofosbuvir
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	10,720	10,720
Accumulated Amortization	1,981	1,456
Intangible asset - Ranexa
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	688	688
Accumulated Amortization	437	363
Other
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	455	455
Accumulated Amortization	$ 260	$ 229