Income Taxes Income Taxes (Tables)

9 Months Ended

Sep. 30, 2018

Income Tax Disclosure [Abstract]

Schedule of Effective Income Tax Rate Reconciliation

The following table presents a reconciliation of the federal statutory corporate income tax rate to the effective income tax rate for the three and nine months ended September 30, 2018 and 2017:

	Ameren			Ameren Missouri			Ameren Illinois
Three Months	2018		2017	2018		2017	2018		2017
Federal statutory corporate income tax rate:	21%		35%	21%		35%	21%		35%
Increases (decreases) from:
Amortization of excess deferred taxes	(6)		—	(7)	(a)	—	(3)		—
Other depreciation differences	—		1	—		1	(1)		(2)
Amortization of deferred investment tax credit	(1)		(1)	—		(1)	—		—
State tax	6		7	4		3	5		7
TCJA	3	(b)	—	—		—	4	(b)	—
Other permanent items	—		(1)	—		—	—		—
Effective income tax rate	23%		41%	18%		38%	26%		40%

Nine Months
Federal statutory corporate income tax rate:	21%		35%	21%		35%	21%		35%
Increases (decreases) from:
Amortization of excess deferred taxes	(3)		—	(4)	(a)	—	(4)		—
Other depreciation differences	—		—	—		1	—		—
Amortization of deferred investment tax credit	(1)		(1)	—		(1)	—		—
State tax	6		6	4		3	7		5
TCJA	1	(b)	—	—		—	1	(b)	—
Other permanent items	(1)		(1)	—		—	—		—
Effective income tax rate	23%		39%	21%		38%	25%		40%

(a) Based on an order issued by the MoPSC in July 2018, Ameren Missouri began amortizing excess deferred taxes in August 2018. See Note 2 – Rate and Regulatory Matters for additional information.

(b) The Ameren Companies updated their respective provisional estimates recorded related to TCJA, as discussed below.