Significant Accounting Policies - Recently Adopted Accounting Pronouncements (Details) - USD ($) $ in Millions	Dec. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
Assets
Prepaid expenses and other current assets	$ 46	$ 53	$ 54
Right-of-use assets	107	110
Liabilities [Abstract]
Accrued liabilities	379	350	322
Long-term lease liabilities	100	103
Other long-term liabilities	$ 67	67	$ 89
ASU 2016-02
Assets
Prepaid expenses and other current assets		(1)
Right-of-use assets		110
Liabilities [Abstract]
Accrued liabilities		28
Long-term lease liabilities		103
Other long-term liabilities		$ (22)