Lease Obligations - Schedule of Future Minimum Lease Payments for Operating and Finance Lease Obligations (Detail) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Operating leases
2019	$ 75
2020	85
2021	74
2022	67
2023	56
After 2023	332
Total lease payments	689
Less: Interest	(270)
Present value of lease liabilities	419
Finance leases
2019	10
2020	12
2021	11
2022	11
2023	11
After 2023	44
Total lease payments	99
Less: Interest	(27)
Present value of lease liabilities	72
Operating and financing leases
2019	85
2020	97
2021	85
2022	78
2023	67
After 2023	376
Total lease payments	788
Less: Interest	(297)
Present value of lease liabilities	$ 491	$ 74