Debt (Details) (USD $)	3 Months Ended							3 Months Ended					3 Months Ended			3 Months Ended		3 Months Ended		3 Months Ended		3 Months Ended		3 Months Ended		3 Months Ended		3 Months Ended		3 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Dec. 31, 2013 Minimum [Member]	Dec. 31, 2013 Maximum [Member]	Dec. 31, 2013 First Facility Regulated Operations [Member]	Dec. 31, 2013 Second Facility Regulated Operations [Member]	Dec. 31, 2013 Third Facility Regulated Operations [Member]	Dec. 31, 2013 Intercompany Facility Regulated Operations [Member]	Dec. 31, 2013 Committed Facility Nonregulated Operations [Member]	Sep. 30, 2013 Committed Facility Nonregulated Operations [Member]	Jan. 29, 2014 Uncommitted Facility Nonregulated Operations [Member]	Dec. 31, 2013 Uncommitted Facility Nonregulated Operations [Member]	Dec. 31, 2013 Intercompany Facility Nonregulated Operations [Member]	Dec. 31, 2013 Nonregulated Facilities [Member]	Dec. 31, 2013 Regulated Facilities [Member]	Dec. 31, 2013 Unsecured Senior Notes Due 2014 [Member]	Sep. 30, 2013 Unsecured Senior Notes Due 2014 [Member]	Dec. 31, 2013 Unsecured Senior Notes Due 2017 [Member]	Sep. 30, 2013 Unsecured Senior Notes Due 2017 [Member]	Dec. 31, 2013 Unsecured Senior Notes Due 2019 [Member]	Sep. 30, 2013 Unsecured Senior Notes Due 2019 [Member]	Dec. 31, 2013 Unsecured Senior Notes Due 2034 [Member]	Sep. 30, 2013 Unsecured Senior Notes Due 2034 [Member]	Dec. 31, 2013 Unsecured Senior Notes Due 2041 [Member]	Sep. 30, 2013 Unsecured Senior Notes Due 2041 [Member]	Dec. 31, 2013 Unsecured Senior Notes Due 2043 [Member]	Sep. 30, 2013 Unsecured Senior Notes Due 2043 [Member]	Dec. 31, 2013 Medium Term Notes Due 2025 [Member]	Sep. 30, 2013 Medium Term Notes Due 2025 [Member]	Dec. 31, 2013 Unsecured Debentures Due 2028 [Member]	Sep. 30, 2013 Unsecured Debentures Due 2028 [Member]
Debt Instrument [Line Items]
Debt Instrument Carrying Amount	$ 2,460,000,000	$ 2,460,000,000														$ 500,000,000	$ 500,000,000	$ 250,000,000	$ 250,000,000	$ 450,000,000	$ 450,000,000	$ 200,000,000	$ 200,000,000	$ 400,000,000	$ 400,000,000	$ 500,000,000	$ 500,000,000	$ 10,000,000	$ 10,000,000	$ 150,000,000	$ 150,000,000
Debt Instrument, Interest Rate, Stated Percentage																4.95%		6.35%		8.50%		5.95%		5.50%		4.15%		6.67%		6.75%
Debt Instrument, Maturity Date																Oct. 15, 2014		Jun. 15, 2017		Mar. 15, 2019		Oct. 15, 2034		Jun. 15, 2041		Jan. 15, 2043		Dec. 15, 2025		Jul. 15, 2028
Debt Instrument, Unamortized Discount	4,250,000	4,329,000
Current maturities of long-term debt	500,000,000	0
Long-term debt	1,955,750,000	2,455,671,000
Line Of Credit Facility [Line Items]
Line Of Credit Facility Maximum Borrowing Capacity	1,000,000,000				950,000,000	25,000,000	10,000,000	500,000,000	15,000,000	25,000,000	50,000,000	25,000,000	500,000,000		985,000,000
Line of Credit Facility, Current Available Borrowing Capacity							4,100,000							15,400,000
Line of Credit Facility, Maximum Borrowing Capacity with Accordion Feature					1,200,000,000.0
Line Of Credit Facility Description								which bears interest at the lower of (i) the Eurodollar rate under the five-year revolving credit facility or (ii) the rate outstanding under the commercial paper program					This facility bears interest at a rate equal to the one-month LIBOR rate plus 3.00 percent or (ii) the rate for AEM's borrowings under its committed credit facility plus 0.75 percent.
Debt Instrument, Covenant, Excess Debt Trigger			15,000,000	100,000,000
Long Term Debt Other Disclosures [Abstract]
Authorized Commercial Paper	950,000,000
Commercial Paper	689,800,000	368,000,000
Debt and Equity Securities Authorized for Issuance	1,750,000,000.00
Debt And Equity Securities Available For Issuance	$ 1,750,000,000.00
Regulated Operations Line of Credit Facilities, Covenant Terms	We are required by the financial covenants in each of these facilities to maintain, at the end of each fiscal quarter, a ratio of total debt to total capitalization of no greater than 70 percent.
Ratio of Total Debt to Total Capital	56.00%
Debt Instrument Covenant Description	In addition to these financial covenants, our credit facilities and public indentures contain usual and customary covenants for our business, including covenants substantially limiting liens, substantial asset sales and mergers. Additionally, our public debt indentures relating to our senior notes and debentures, as well as our revolving credit agreements, each contain a default provision that is triggered if outstanding indebtedness arising out of any other credit agreements in amounts ranging from in excess of $15 million to in excess of $100 million becomes due by acceleration or is not paid at maturity.
Debt Instrument Covenant Compliance	We were in compliance with all of our debt covenants as of December 31, 2013.