Significant Accounting Policies - Additional Information Related to Leases (Details) - USD ($) $ in Millions			6 Months Ended
		Jan. 01, 2019	Jun. 30, 2019
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash outflows from operating leases			$ 14
Operating cash outflows from finance lease			2
Financing cash outflows from finance lease	[1]		3
Right-of-use assets obtained in exchange for lease liabilities:
Operating leases		$ 88	97	[2]
Finance lease	[3]		$ 88
Weighted-average remaining lease term:
Operating leases			4 years 9 months 18 days
Finance lease			11 years 6 months
Weighted-average discount rate:
Operating leases			4.32%
Finance lease			4.49%

[1] Amount is included in other financing activities, net on the unaudited condensed consolidated statement of cash flows.

[2] Amount includes operating leases existing on January 1, 2019 of $88 million and those that commenced during the six months ended June 30, 2019 of $9 million.

[3] Amount represents the finance lease liability arising from obtaining the ROU asset related to our Headquarters Lease, which was recognized upon the adoption of ASC 842 on January 1, 2019.