Leases - Summary of Cash Flows Related to Leases (Details)	3 Months Ended
	Mar. 31, 2019 USD ($)
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	$ 36,000,000
Operating cash flows from finance leases (less than $1 million)	1,000,000
Financing cash flows from finance leases (less than $1 million)	1,000,000
Right-of-use assets obtained in exchange for lease obligations:
Operating leases	28,000,000
Finance leases	$ 0