New Accounting Standard - Leases Presented in Balance Sheet (Details) - USD ($)	Mar. 31, 2019	Jan. 01, 2019
Assets and Liabilities, Lessee [Abstract]
Lease right-of-use assets (included in property, plant, equipment and mine development costs, net)	$ 245,000,000	$ 243,000,000
Short-term lease liabilities (included in accounts payable and accrued liabilities)	33,000,000
Long-term lease liabilities (included in other liabilities)	223,000,000
Total lease liabilities	$ 256,000,000	$ 243,000,000