CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED) - USD ($) $ in Thousands	6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Cash Flows From Operating Activities
Net income	$ 493,124	$ 289,760
Adjustments to reconcile net income to net cash provided by operating activities:
Charged to depreciation and amortization	177,755	154,810
Deferred income taxes	116,023	148,657
One-Time Income Tax Benefit, TCJA	(165,675)	0
Gain on sale of discontinued operations	0	(12,931)
Discontinued cash flow hedging for natural gas marketing commodity contracts	0	(10,579)
Other	12,252	10,391
Net assets / liabilities from risk management activities	812	26,757
Net change in operating assets and liabilities	117,076	(54,862)
Net cash provided by operating activities	751,367	552,003
Cash Flows From Investing Activities
Capital expenditures	(693,978)	(559,385)
Acquisition	0	(85,714)
Proceeds from the sale of discontinued operations	3,000	133,560
Available-for-sale securities activities, net	(1,175)	(8,918)
Other, net	4,009	3,787
Net cash used in investing activities	(688,144)	(516,670)
Cash Flows From Financing Activities
Net increase in short-term debt	(318,143)	(159,204)
Net proceeds from equity offering	395,092	49,400
Issuance of common stock through stock purchase and employee retirement plans	11,902	16,984
Proceeds from issuance of long-term debt, net of discount	0	125,000
Interest rate agreements cash collateral	0	25,670
Cash dividends paid	(105,891)	(95,314)
Repurchase of equity awards	(1,518)	0
Net cash provided by (used in) financing activities	(18,558)	(37,464)
Net increase (decrease) in cash and cash equivalents	44,665	(2,131)
Cash and cash equivalents at beginning of period	26,409	47,534
Cash and cash equivalents at end of period	$ 71,074	$ 45,403