Calico (Details) $ in Millions	49 Months Ended
	Sep. 30, 2017 USD ($)
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Payments to acquire interest in joint venture	$ 240
Commitment to Invest
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Research commitments	490
Research and development arrangement | AbbVie Inc
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Accumulated payments for research and development commitment	750
Research and development arrangement | Calico
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Research commitments	500
Accumulated payments for research and development commitment	$ 250