Basis of Presentation - Schedule of Impact of adoption on Consolidated Balance Sheet (Detail) - USD ($) $ in Millions	Mar. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
Assets
Property, plant and equipment — net	$ 15,898		$ 16,083
Operating lease right-of-use assets — net	713		0
Finance lease right-of-use assets — net	332		0
Liabilities
Accrued liabilities	1,369		1,560
Current maturities of long-term debt	12		67
Current portion of operating and finance lease obligations	402		0
Long-term debt	6,550		6,605
Long-term operating lease obligations	436		0
Long-term finance lease obligations	250		0
Other liabilities and deferred credits	$ 491		$ 575
ASC 842
Assets
Property, plant and equipment — net		$ 15,737
Operating lease right-of-use assets — net		804
Finance lease right-of-use assets — net		346
Liabilities
Accrued liabilities		1,558
Current maturities of long-term debt		12
Current portion of operating and finance lease obligations		437
Long-term debt		6,351
Long-term operating lease obligations		516
Long-term finance lease obligations		254
Other liabilities and deferred credits		483
ASC 842 | Adjustment For Finance Leases
Assets
Property, plant and equipment — net		(346)
Operating lease right-of-use assets — net		0
Finance lease right-of-use assets — net		346
Liabilities
Accrued liabilities		0
Current maturities of long-term debt		(55)
Current portion of operating and finance lease obligations		55
Long-term debt		(254)
Long-term operating lease obligations		0
Long-term finance lease obligations		254
Other liabilities and deferred credits		0
ASC 842 | Adjustment For Operating Leases
Assets
Property, plant and equipment — net		0
Operating lease right-of-use assets — net		804
Finance lease right-of-use assets — net		0
Liabilities
Accrued liabilities		(2)
Current maturities of long-term debt		0
Current portion of operating and finance lease obligations		382
Long-term debt		0
Long-term operating lease obligations		516
Long-term finance lease obligations		0
Other liabilities and deferred credits		$ (92)