Lease Obligations - Schedule of Future Minimum Lease Payments for Operating and Finance Lease Obligations (Detail) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Operating leases
2019	$ 46
2020	86
2021	77
2022	69
2023	58
After 2023	322
Total lease payments	658
Less: Interest	(254)
Present value of lease liabilities	404
Finance leases
2019	6
2020	12
2021	11
2022	11
2023	11
After 2023	46
Total lease payments	97
Less: Interest	(26)
Present value of lease liabilities	71
Operating and financing leases
2019	52
2020	98
2021	88
2022	80
2023	69
After 2023	368
Total lease payments	755
Less: Interest	(280)
Present value of lease liabilities	$ 475	$ 74