Consolidated Statements of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash flows from operating activities
Net income	$ 285.7	$ 276.3	$ 260.3
Adjustments to reconcile net income to net cash from operating activities:
Depreciation and amortization	328.3	313.5	302.6
Deferred income taxes and investment tax credits	87.7	118.9	92.2
Allowance for other funds used during construction	(24.1)	(17.2)	(10.5)
Deferred recovery clauses	54.4	26.5	(16.2)
Receivables, less allowance for uncollectibles	17.7	(3.0)	0.4
Inventories	16.0	(21.3)	13.1
Prepayments and other deposits	(0.1)	(4.0)	1.5
Taxes accrued	67.5	(17.2)	11.8
Interest accrued	(0.7)	(0.1)	0.6
Accounts payable	63.1	(26.8)	5.9
Other	(64.9)	(37.7)	(14.5)
Cash flows from operating activities	830.6	607.9	647.2
Cash flows from investing activities
Capital expenditures	(726.8)	(686.6)	(671.0)
Net proceeds from sale of assets	9.1	0.0	0.0
Cash flows used in investing activities	(717.7)	(686.6)	(671.0)
Cash flows from financing activities
Common stock	150.0	175.0	100.0
Proceeds from long-term debt issuance	0.0	251.1	296.3
Repayment of long-term debt	(83.3)	(83.3)	(83.3)
Net change in short-term debt	109.0	3.0	(26.0)
Dividends	(288.2)	(268.4)	(262.6)
Cash flows from/(used in) financing activities	(112.5)	77.4	24.4
Net increase (decrease) in cash and cash equivalents	0.4	(1.3)	0.6
Cash and cash equivalents at beginning of the year	9.1	10.4	9.8
Cash and cash equivalents at end of the year	9.5	9.1	10.4
Supplemental disclosure of cash paid (received)
Interest	102.9	106.2	102.5
Income taxes	(3.0)	63.7	52.6
Supplemental disclosure of non-cash activities
Change in accrued capital expenditures	$ (8.9)	$ 6.9	$ 14.3