Income Taxes (Tables)

12 Months Ended

Dec. 31, 2016

Income Tax Disclosure [Abstract]

Schedule Of Income Tax Expense (Benefit)

	Year Ended December 31,
	2016			2015			2014
	(Millions)
Current income tax expense (benefit):
U.S. federal	$	5		$	(243	)	$	152
Various states		(11	)		(8	)		18
Canada and various provinces		106			14			307
Total current tax expense (benefit)		100			(237	)		477
Deferred income tax expense (benefit):
U.S. federal		(3	)		(5,033	)		1,610
Various states		—			(336	)		93
Canada and various provinces		(270	)		(459	)		188
Total deferred tax expense (benefit)		(273	)		(5,828	)		1,891
Total income tax expense (benefit)	$	(173	)	$	(6,065	)	$	2,368

Schedule Of Effective Income Tax Rate Reconciliation

	Year Ended December 31,
	2016			2015			2014
	(Millions)
Total income tax expense (benefit)	$	(173	)	$	(6,065	)	$	2,368
U.S. statutory income tax rate		35	%		35	%		35	%
Deferred tax asset valuation allowance		(22	%)		(4	%)		0	%
Non-deductible goodwill and intangible impairment		(8	%)		(2	%)		23	%
Change in unrecognized tax benefits		(2	%)		0	%		1	%
Taxation on Canadian operations		(3	%)		(1	%)		(4	%)
State income taxes		1	%		1	%		2	%
Other		3	%		0	%		1	%
Effective income tax rate		4	%		29	%		58	%

Schedule Of Deferred Tax Assets And Liabilities

	December 31,
	2016			2015
	(Millions)
Deferred tax assets:
Property and equipment	$	685		$	490
Asset retirement obligations		488			485
Accrued liabilities		130			160
Net operating loss carryforwards		777			175
Pension benefit obligations		98			106
Other		203			162
Total deferred tax assets before valuation allowance		2,381			1,578
Less: valuation allowance		(1,666	)		(967	)
Net deferred tax assets		715			611
Deferred tax liabilities:
Property and equipment		(884	)		(1,187	)
Long-term debt		(53	)		(36	)
Other		(426	)		(271	)
Total deferred tax liabilities		(1,363	)		(1,494	)
Net deferred tax liability	$	(648	)	$	(883	)

Schedule Of Changes In Unrecognized Tax Benefits

	December 31,
	2016			2015
	(Millions)
Balance at beginning of year	$	131		$	241
Tax positions taken in prior periods		36			(19	)
Tax positions taken in current year		—			31
Accrual of interest related to tax positions taken		39			(5	)
Settlements		—			(108	)
Lapse of statute of limitations		(5	)		—
Foreign currency translation		1			(9	)
Balance at end of year	$	202		$	131

Summary Of The Tax Years By Jurisdiction That Remain Subject To Examination By Taxing Authorities

Jurisdiction	Tax Years Open
U.S. Federal	2012-2016
Various U.S. states	2010-2016
Canada Federal	2003-2016
Various Canadian provinces	2003-2016