CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Operating activities
Net income	$ 183,893	$ 203,569
Remove income from discontinued operations	(124)	(102)
Adjustments to reconcile net income to cash provided by operating activities:
Depreciation and amortization	233,097	229,217
Conservation and demand side management program amortization	1,882	3,024
Nuclear fuel amortization	26,000	25,551
Deferred income taxes	167,426	114,852
Amortization of investment tax credits	(1,552)	(1,580)
Allowance for equity funds used during construction	(13,450)	(13,244)
Equity earnings of unconsolidated subsidiaries	(7,158)	(7,713)
Dividends from unconsolidated subsidiaries	8,028	8,454
Share-based compensation expense	3,883	9,895
Net derivative losses	7,133	14,495
Changes in operating assets and liabilities:
Accounts receivable	(52,643)	(46,947)
Accrued unbilled revenues	197,330	157,996
Inventories	143,873	118,595
Other current assets	(71,547)	43,551
Accounts payable	(202,649)	(72,424)
Net regulatory assets and liabilities	61,872	17,853
Other current liabilities	17,711	5,491
Pension and other employee benefit obligations	(180,030)	(134,004)
Change in other noncurrent assets	(38,806)	10,520
Change in other noncurrent liabilities	(6,686)	(27,606)
Net cash provided by operating activities	477,483	659,443
Investing activities
Utility capital/construction expenditures	(497,218)	(540,339)
Allowance for equity funds used during construction	13,450	13,244
Merricourt deposit	0	(90,833)
Purchase of investments in external decommissioning fund	(213,618)	(699,156)
Proceeds from the sale of investments in external decommissioning fund	213,618	699,156
Investment in WYCO Development LLC	(172)	(901)
Change in restricted cash	86,232	26
Other, net	(1,304)	(5,545)
Net cash used in investing activities	(399,012)	(624,348)
Financing activities
Proceeds from short-term borrowings, net	120,000	65,100
Proceeds from issuance of long-term debt	745	0
Repayments of long-term debt, including reacquisition premiums	(758)	(551)
Proceeds from issuance of common stock	1,598	1,878
Repurchase of common stock	(18,529)	0
Purchase of common stock for settlement of equity awards	(23,307)	0
Dividends paid	(119,162)	(115,621)
Net cash used in financing activities	(39,413)	(49,194)
Net change in cash and cash equivalents	39,058	(14,099)
Cash and cash equivalents at beginning of period	60,684	108,437
Cash and cash equivalents at end of period	99,742	94,338
Supplemental disclosure of cash flow information:
Cash paid for interest (net of amounts capitalized)	(156,275)	(150,473)
Cash (paid) received for income taxes, net	(1,173)	59,051
Supplemental disclosure of non-cash investing and financing transactions:
Property, plant and equipment additions in accounts payable	224,316	116,145
Issuance of common stock for reinvested dividends and 401(k) plans	$ 18,815	$ 20,419