Basis of Presentation and Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2018

Accounting Policies [Abstract]

Schedule of unproved properties excluded from the amortization base

The table below sets forth the cost of unproved properties excluded from the amortization base as of December 31, 2018 and the year in which the associated costs were incurred:

	Year of Acquisition
	2018		2017		2016		Prior		Total
	($ in millions)
Leasehold cost	$	24	$	31	$	40	$	1,577	$	1,672
Exploration cost	122		—		2		—		124
Capitalized interest	125		84		63		269		541
Total	$	271	$	115	$	105	$	1,846	$	2,337