II-Valuation and Qualifying Accounts (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017		Dec. 31, 2016
Price-risk management credit reserves-liabilities [Member]
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
SEC Schedule, 12-09, Valuation Allowances and Reserves, Amount	[1],[2]		$ 0	$ 4		$ 5
SEC Schedule, 12-09, Valuation Allowances and Reserves, Additions, Charge to Cost and Expense	[1],[2]		0	0
SEC Schedule, 12-09, Valuation Allowances and Reserves, Period Increase (Decrease)	[1],[2]		(4)	(1)
SEC Schedule, 12-09, Valuation Allowances and Reserves, Deduction	[1],[2]		0	0
SEC Schedule, 12-09, Allowance, Notes Receivable
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
SEC Schedule, 12-09, Valuation Allowances and Reserves, Amount	[3]	$ 9	0	2		3
SEC Schedule, 12-09, Valuation Allowances and Reserves, Additions, Charge to Cost and Expense	[3]	9	0	0
SEC Schedule, 12-09, Valuation Allowances and Reserves, Period Increase (Decrease)	[3]	0	0	0
SEC Schedule, 12-09, Valuation Allowances and Reserves, Deduction	[3]	0	2	1
SEC Schedule, 12-09, Valuation Allowance, Deferred Tax Asset [Member]
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
SEC Schedule, 12-09, Valuation Allowances and Reserves, Amount	[3]	216	213	195	[4]	$ 151	[4]
SEC Schedule, 12-09, Valuation Allowances and Reserves, Additions, Charge to Cost and Expense	[3]	3	18	44	[4]
SEC Schedule, 12-09, Valuation Allowances and Reserves, Period Increase (Decrease)	[3]	0	0	0	[4]
SEC Schedule, 12-09, Valuation Allowances and Reserves, Deduction	[3]	$ 0	$ 0	$ 0	[4]

[1] Deducted from related liabilities.

[2] Included in revenues.

[3] Deducted from related assets.

[4] Includes impact of the Tax Cuts and Jobs Act enacted rate reduction