Lease Obligations - Schedule of Future Minimum Lease Payments for Operating and Finance Lease Obligations (Detail) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Operating leases
2019	$ 26
2020	93
2021	81
2022	69
2023	55
After 2023	335
Total lease payments	659
Less: Interest	(266)
Present value of lease liabilities	393
Finance leases
2019	2
2020	12
2021	11
2022	11
2023	11
After 2023	46
Total lease payments	93
Less: Interest	(24)
Present value of lease liabilities	69
Operating and financing leases
2019	28
2020	105
2021	92
2022	80
2023	66
After 2023	381
Total lease payments	752
Less: Interest	(290)
Present value of lease liabilities	$ 462	$ 74