Significant Accounting Policies - Recent Accounting Pronouncements (Details) - USD ($) $ in Millions	Dec. 31, 2019	Jan. 01, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease, right-of-use asset	$ 1,000
Operating lease, liability	1,105
Operating lease, liability, noncurrent	$ 855
ASU 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease, right-of-use asset		$ 1,000
Operating lease, liability		1,100
Operating lease, liability, noncurrent		$ 830