Income Taxes (Tables)

12 Months Ended

Dec. 31, 2018

Income Tax Disclosure [Abstract]

Schedule of Remeasurement of Deferred Incomes Taxes due to the Tax Cuts and Jobs Act [Table Text Block]

	Ameren Missouri			Ameren Illinois			Other			Ameren
Increase (Decrease)
Accumulated deferred income taxes, net	$	(1,419	)	$	(871	)	$	37		$	(2,253	)
Income tax expense (benefit)	32			(5		)	127			154
Noncurrent regulatory assets	(89		)	(24		)	(1		)	(114		)
Noncurrent regulatory liabilities	1,362			842			89			2,293

Schedule Of Effective Income Tax Rate Reconciliation

The following table presents the principal reasons for the difference between the effective income tax rate and the federal statutory corporate income tax rate for the years ended December 31, 2018, 2017, and 2016:

	Ameren Missouri		Ameren Illinois		Ameren
2018
Federal statutory corporate income tax rate:	21	%	21	%	21	%
Increases (decreases) from:
Amortization of excess deferred taxes	(4	)	(4	)	(4	)
Other depreciation differences	—		(1	)	—
Amortization of deferred investment tax credit	(1	)	—		(1	)
State tax	4		7		6
TCJA	1		1		1
Tax credits	(1	)	—		—
Other permanent items	—		—		(1	)
Effective income tax rate	20	%	24	%	22	%
2017
Federal statutory corporate income tax rate:	35	%	35	%	35	%
Increases (decreases) from:
Depreciation differences	1		(1	)	—
Amortization of deferred investment tax credit	(1	)	—		(1	)
State tax	4		6		6
TCJA	6		(1	)	14
Tax credits	(1	)	—		—
Other permanent items	—		(1	)	(2	)
Effective income tax rate	44	%	38	%	52	%
2016
Federal statutory corporate income tax rate:	35	%	35	%	35	%
Increases (decreases) from:
Depreciation differences	1		—		—
Amortization of deferred investment tax credit	(1	)	—		—
State tax	3		5		4
Stock-based compensation(a)	—		—		(2	)
Valuation allowance	—		—		1
Other permanent items	—		(2	)	(1	)
Effective income tax rate	38	%	38	%	37	%

(a) Reflects the adoption of authoritative accounting guidance related to stock-based compensation, which resulted in the recognition of a $21 million income tax benefit in 2016.

Schedule Of Components Of Income Tax Expense (Benefit)

The following table presents the components of income tax expense for the years ended December 31, 2018, 2017, and 2016:

	Ameren Missouri			Ameren Illinois			Other			Ameren
2018
Current taxes:
Federal	$	104		$	4		$	(118	)	$	(10	)
State	29			6			(12		)	23
Deferred taxes:
Federal	22			75			123			220
State	(2		)	28			23			49
Amortization of excess deferred taxes	(24		)	(15		)	(1		)	(40		)
Amortization of deferred investment tax credits	(5		)	—			—			(5		)
Total income tax expense	$	124		$	98		$	15		$	237
2017
Current taxes:
Federal	$	149		$	(34	)	$	(110	)	$	5
State	23			29			(20		)	32
Deferred taxes:
Federal	76			185			250			511
State	11			(13		)	36			34
Amortization of deferred investment tax credits	(5		)	(1		)	—			(6		)
Total income tax expense	$	254		$	166		$	156		$	576
2016
Current taxes:
Federal	$	31		$	(8	)	$	(24	)	$	(1	)
State	6			12			(21		)	(3		)
Deferred taxes:
Federal	161			117			21			299
State	23			37			32			92
Amortization of deferred investment tax credits	(5		)	—			—			(5		)
Total income tax expense	$	216		$	158		$	8		$	382

Schedule Of Deferred Tax Assets And Liabilities Resulting From Temporary Differences

The following table presents the accumulated deferred income tax assets and liabilities recorded as a result of temporary differences at December 31, 2018 and 2017:

	Ameren Missouri			Ameren Illinois			Other			Ameren
2018
Accumulated deferred income taxes, net liability (asset):
Plant-related	$	2,010		$	1,345		$	179		$	3,534
Regulatory assets and liabilities, net	(343		)	(221		)	(25		)	(589		)
Deferred employee benefit costs	(58		)	(4		)	(64		)	(126		)
Tax carryforwards	(35		)	(26		)	(166		)	(227		)
Other	(40		)	25			46			31
Total net accumulated deferred income tax liabilities (assets)	$	1,534		$	1,119		$	(30	)	$	2,623
2017
Accumulated deferred income taxes, net liability (asset):
Plant-related	$	2,064		$	1,264		$	146		$	3,474
Regulatory assets and liabilities, net	(317		)	(206		)	(24		)	(547		)
Deferred employee benefit costs	(53		)	(17		)	(61		)	(131		)
Revenue requirement reconciliation adjustments	—			20			—			20
Tax carryforwards	(31		)	(43		)	(287		)	(361		)
Other	(13		)	3			61			51
Total net accumulated deferred income tax liabilities (assets)	$	1,650		$	1,021		$	(165	)	$	2,506

Schedule Of Net Operating Loss Carryforwards And Tax Credit Carryforwards

The following table presents the components of accumulated deferred income tax assets relating to net operating loss carryforwards, tax credit carryforwards, and charitable contribution carryforwards at December 31, 2018 and 2017:

	Ameren Missouri		Ameren Illinois		Other			Ameren
2018
Net operating loss carryforwards:
Federal(a)	$	—	$	23	$	55		$	78
State(a)	—		—		13			13
Total net operating loss carryforwards	$	—	$	23	$	68		$	91
Tax credit carryforwards:
Federal(b)	$	35	$	3	$	79		$	117
State(c)	—		—		10			10
Total tax credit carryforwards	$	35	$	3	$	89		$	127
Charitable contribution carryforwards(d)	$	—	$	—	$	14		$	14
Valuation allowance(e)	—		—		(5		)	(5		)
Total charitable contribution carryforwards	$	—	$	—	$	9		$	9
2017
Net operating loss carryforwards:
Federal	$	—	$	41	$	162		$	203
State	—		—		32			32
Total net operating loss carryforwards	$	—	$	41	$	194		$	235
Tax credit carryforwards:
Federal	$	31	$	2	$	80		$	113
State	—		—		7			7
Total tax credit carryforwards	$	31	$	2	$	87		$	120
Charitable contribution carryforwards	$	—	$	—	$	11		$	11
Valuation allowance	—		—		(5		)	(5		)
Total charitable contribution carryforwards	$	—	$	—	$	6		$	6

(a) Will expire between 2034 and 2037. Any net operating loss carryforward generated after January 1, 2018, will not have an expiration date as a result of the TCJA.

(b) Will expire between 2029 and 2037.

(c) Will expire between 2019 and 2022.

(d) Will expire between 2019 and 2023.

(e) See Schedule II under Part IV, Item 15, in this report for information on changes in the valuation allowance.