NiSource (NI) 10-K 18 Feb 16 2015 FY Annual report Financial data

Document And Entity Information

Document And Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2015	Feb. 10, 2016	Jun. 30, 2015
Document Information [Line Items]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2015
Document Fiscal Year Focus	2,015
Document Fiscal Period Focus	FY
Entity Registrant Name	NISOURCE INC/DE
Entity Central Index Key	1,111,711
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 14,408,583,291
Entity Common Stock, Shares Outstanding		319,741,768

Statements Of Consolidated Inco

Statements Of Consolidated Income - USD ($) shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Net Revenues
Gas Distribution	$ 2,081.9	$ 2,597.8	$ 2,226.3
Gas Transportation and Storage	969.8	987.4	820
Electric	1,572.9	1,672	1,563.4
Other	27.2	15.2	15.7
Gross Revenues	4,651.8	5,272.4	4,625.4
Cost of Sales (excluding depreciation and amortization)	1,643.7	2,372.9	1,963
Total Net Revenues	3,008.1	2,899.5	2,662.4
Operating Expenses
Operation and maintenance	1,426.1	1,367.3	1,254.4
Depreciation and amortization	524.4	486.9	470.4
Loss on sale of assets and impairments, net	1.6	3	1.1
Other taxes	256.1	253.2	238.4
Total Operating Expenses	2,208.2	2,110.4	1,964.3
Operating Income	799.9	789.1	698.1
Other Income (Deductions)
Interest expense, net	(380.2)	(379.5)	(375.3)
Other, net	17.4	13.4	6.8
Loss on early extinguishment of long-term debt	(97.2)	0	0
Total Other Deductions	(460)	(366.1)	(368.5)
Income from Continuing Operations before Income Taxes	339.9	423	329.6
Income Taxes	141.3	166.8	108.6
Income from Continuing Operations	198.6	256.2	221
Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	103.5	273.8	276.2
Gain on Disposition of Discontinued Operations - net of taxes	0	0	34.9
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	302.1	530	532.1
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Noncontrolling Interest	15.6	0	0
Net Income	286.5	530	532.1
Income from Discontinued Operations - net of taxes	$ 87.9	$ 273.8	$ 311.1
Basic Earnings (Loss) Per Share ($)
Continuing Operations	$ 0.63	$ 0.81	$ 0.71
Discontinued operations	0.27	0.87	0.99
Basic Earnings Per Share	0.90	1.68	1.70
Diluted Earnings (Loss) Per Share ($)
Continuing operations	0.63	0.81	0.71
Discontinued operations	0.27	0.86	0.99
Diluted Earnings Per Share	$ 0.90	$ 1.67	$ 1.70
Basic Average Common Shares Outstanding	317,746	315,120	312,402
Diluted Average Common Shares	319,836	316,636	313,646

Statements of Consolidated Comp

Statements of Consolidated Comprehensive Income - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Noncontrolling Interest		$ 15.6	$ 0	$ 0
Comprehensive Income (Loss):
Net Income		286.5	530	532.1
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest		302.1	530	532.1
Net unrealized gain (loss) on available-for-sale securities	[1]	(0.8)	0.6	(2.9)
Net unrealized gain on cash flow hedges	[2]	(7.8)	2.2	2.8
Unrecognized pension and OPEB (costs) benefit	[3]	(2.4)	(9.8)	22
Total Other Comprehensive (Loss) Income		(11)	(7)	21.9
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest		291.1	523	554
Total comprehensive income		$ 275.5	$ 523	$ 554
[1]	Net unrealized gain (loss) on available-for-sale securities, net of $0.4 million tax benefit, $0.3 million tax expense and $1.5 million tax benefit in 2015, 2014 and 2013, respectively.
[2]	Net unrealized gain on derivatives qualifying as cash flow hedges, net of $4.8 million tax benefit, and $1.5 million and $1.8 million tax expense in 2015, 2014 and 2013, respectively.
[3]	Unrecognized pension and OPEB benefit (costs), net of $4.6 million and $2.5 million tax benefit, and $14.3 million tax expense in 2015, 2014 and 2013, respectively.

Statements of Consolidated Com4

Statements of Consolidated Comprehensive Income (Parenthetical) - Parent Company [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Tax	$ (0.4)	$ 0.3	$ (1.5)
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Tax	(4.8)	1.5	1.8
Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Tax	$ 4.6	$ 2.5	$ (14.3)

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Property, Plant and Equipment
Utility Plant	$ 18,946.9	$ 17,668.4
Accumulated depreciation and amortization	(6,853.4)	(6,629.5)
Net utility plant	12,093.5	11,038.9
Other property, at cost, less accumulated depreciation	18	18.5
Net Property, Plant and Equipment	12,111.5	11,057.4
Investments and Other Assets
Unconsolidated affiliates	6.9	8.3
Other investments	187.7	204.8
Total Investments and Other Assets	194.6	213.1
Current Assets
Cash and cash equivalents	15.5	24.9
Restricted cash	29.7	24.9
Accounts receivable (less reserve of $20.3 and $24.9, respectively)	660	920.8
Gas inventory	343.5	440.3
Underrecovered gas and fuel costs	34.8	32
Materials and supplies, at average cost	86.8	81.1
Electric production fuel, at average cost	106.3	64.8
Exchange gas receivable	21	28.3
Disposal Group, Including Discontinued Operation, Assets, Current	0	283.4
Regulatory assets	172.1	187.4
Prepayments and other	107.5	106.5
Total Current Assets	1,577.2	2,194.4
Other Assets
Regulatory assets	1,599.8	1,544.5
Goodwill	1,690.7	1,690.7
Intangible assets	253.7	264.7
Disposal Group, Including Discontinued Operation, Assets, Noncurrent	0	7,546
Deferred charges and other	65	79
Total Other Assets	3,609.2	11,124.9
Total Assets	17,492.5	24,589.8
Common Stockholders' Equity
Common stock - $0.01 par value, 400,000,000 shares authorized; 319,110,083 and 316,037,421 shares outstanding, respectively	3.2	3.2
Additional paid-in capital	5,078	4,787.6
Retained earnings	(1,123.3)	1,494
Accumulated other comprehensive loss	(35.1)	(50.6)
Treasury stock	(79.3)	(58.9)
Total Common Stockholders' Equity	3,843.5	6,175.3
Long-term debt, excluding amounts due within one year	5,948.5	8,151.5
Total Capitalization	9,792	14,326.8
Current Liabilities
Current portion of long-term debt	433.7	266.6
Short-term borrowings	567.4	1,576.9
Accounts payable	433.4	610.1
Customer deposits and credits	316.3	280.9
Taxes accrued	183.5	169.2
Interest accrued	129	140.7
Overrecovered gas and fuel costs	148.1	45.6
Exchange gas payable	62.3	101.5
Deferred revenue	6.6	3.4
Regulatory liabilities	83.3	61.1
Accrued liability for postretirement and postemployment benefits	4.9	5.3
Disposal Group, Including Discontinued Operation, Liabilities, Current	0.3	369
Legal and environmental reserves	37.6	22.7
Employee-related Liabilities, Current	136.4	166.8
Other accruals	114.7	144.5
Total Current Liabilities	2,657.5	3,964.3
Other Liabilities and Deferred Credits
Deferred income taxes	2,365.3	2,165.8
Deferred investment tax credits	14.8	17.1
Deferred credits	90.7	100.9
Accrued liability for postretirement and postemployment benefits	759.7	733.9
Disposal Group, Including Discontinued Operation, Liabilities, Noncurrent	0	1,558.4
Regulatory liabilities and other removal costs	1,350.4	1,379.6
Asset retirement obligations	254	136.2
Other noncurrent liabilities	208.1	206.8
Total Other Liabilities and Deferred Credits	5,043	6,298.7
Commitments and Contingencies (Refer to Note 18, Other Commitments and Contingencies)	0	0
Total Capitalization and Liabilities	$ 17,492.5	$ 24,589.8

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Accounts receivable less reserve	$ 20.3	$ 24.9
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	400,000,000	400,000,000
Common stock, shares outstanding	319,110,083	316,037,421

Statements Of Consolidated Cash

Statements Of Consolidated Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	$ 302.1	$ 530	$ 532.1
Adjustments to Reconcile Net Income to Net Cash from Continuing Operations:
Payments of Debt Extinguishment Costs	97.2	0	0
Depreciation and amortization	524.4	486.9	470.4
Net changes in price risk management assets and liabilities	3.7	2.6	2.6
Deferred income taxes and investment tax credits	135.3	161.4	118.4
Deferred revenue	7.2	(0.1)	0.6
Stock compensation expense and 401(k) profit sharing contribution	50.7	66	48.5
Loss on sale of assets and impairment, net	1.6	3	1.1
Income (loss) from unconsolidated affiliates	0.6	0.8	0.5
Gain on disposition of discontinued operations - net of taxes	0	0	(34.9)
Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	(103.5)	(273.8)	(276.2)
Amortization of discount/premium on debt	8.7	10	9.4
AFUDC equity	(11.5)	(10.7)	(11.7)
Accounts receivable	262.2	(42.8)	(97.3)
Income tax receivable	(0.6)	2.3	101.5
Inventories	46.9	(115.9)	(13.1)
Accounts payable	(190.5)	29.9	62.3
Customer deposits and credits	35.5	29.8	(8.2)
Taxes accrued	8.7	4.5	9
Interest accrued	(11.6)	4.3	3.8
Overrecovered gas and fuel costs	99.6	27.9	8.6
Exchange gas receivable/payable	(31.7)	(43.9)	21.5
Other accruals	(55.1)	4.4	1.8
Prepayments and other current assets	0.7	(4.5)	(8.3)
Regulatory assets/liabilities	(17.6)	(255.6)	436.5
Postretirement and postemployment benefits	25.6	136	(435.8)
Deferred credits	(10.1)	9.1	7.8
Deferred charges and other noncurrent assets	5.2	3.9	10.5
Other noncurrent liabilities	(20.3)	(4.3)	6.4
Net Operating Activities from Continuing Operations	1,163.4	761.2	967.8
Net Operating Activities from Discontinued Operations	293.4	558.4	469
Net Cash Flows from Operating Activities	1,456.8	1,319.6	1,436.8
Net Cash Provided by (Used in) Investing Activities [Abstract]
Capital expenditures	(1,360.7)	(1,282.5)	(1,205.1)
Proceeds from disposition of assets	4.5	4.7	2.7
Restricted cash withdrawals (deposits)	(4.8)	(17.1)	38.7
Cash Contributions from Spin Off	3,798.2	0	0
Other investing activities	(62.2)	(18.6)	(58.7)
Net Investing Activities from (used for) Continuing Operations	2,375	(1,313.5)	(1,222.4)
Net Investing Activities used for Discontinued Operations	(430.1)	(803.1)	(669)
Net Cash Flows from (used for) Investing Activities	1,944.9	(2,116.6)	(1,891.4)
Net Cash Provided by (Used in) Financing Activities [Abstract]
Transfer of Cash and Cash Equivalents At Spin Off Net	(136.8)	0	0
Issuance of long-term debt	0	748.4	1,307.6
Repayments of long-term debt and capital lease obligations	(2,092.2)	(521)	(510.9)
Premium and other debt related costs	(93.5)	(8.7)	(3.2)
Change in short-term borrowings, net	(936.4)	878.1	(78.1)
Issuance of common stock	22.5	30.3	43.7
Acquisition of treasury stock	(20.4)	(10.2)	(8.1)
Dividends paid - common stock	(263.4)	(321.3)	(305.9)
Net Cash Provided by (Used in) Financing Activities, Continuing Operations	(3,520.2)	795.6	445.1
Cash Provided by (Used in) Financing Activities, Discontinued Operations	108.6	0	0
Net Cash Flows from (used for) Financing Activities	(3,411.6)	795.6	445.1
Change in cash and cash equivalents from continuing operations	18.2	243.3	190.5
Change in cash and cash equivalents used for discontinued operations	(28.1)	(244.7)	(200)
Cash and cash equivalents at beginning of period	24.9	26.5	35.6
Cash and cash equivalents at beginning of period	15.5	24.9	26.5
Change in cash included in discontinued operations	$ 0.5	$ (0.2)	$ 0.4

Statements Of Consolidated Long

Statements Of Consolidated Long-Term Debt - USD ($) $ in Millions		Dec. 31, 2015	Dec. 31, 2014
Long-Term Notes		$ 6,382.2	$ 8,418.1
Long-term Debt	[1]	6,427.7
Total long-term debt, excluding amount due within one year		5,948.5	8,151.5
Columbia Of Massachusetts [Member]
Medium-Term Notes		40	40
Unamortized issuance costs and discount on long-term debt		(3)	(3.3)
Long-term Debt		37	36.7
Columbia Of Ohio [Member]
Capital lease obligations		138.6	96.4
Long-term Debt		138.6	96.4
NiSource Capital Markets Inc [Member]
Senior Notes		3	3
Medium-Term Notes		106	106
Unamortized issuance costs and discount on long-term debt		(0.7)	(0.8)
Long-term Debt		108.3	108.2
NiSource Corporate Services [Member]
Long-term Debt		2.3	2.5
NiSource Development Company Inc [Member]
NDC Douglas Properties, Inc. - Notes Payable		2.1	2.1
Long-term Debt		2.1	2.1
NiSource Finance Corporation [Member]
Unamortized issuance costs and discount on long-term debt		(41.4)	(49.6)
Long-term Debt		5,423.6	7,531.9
NIPSCO [Member]
Medium-Term Notes		95.5	95.5
Capital lease obligations		45.5	52.8
Unamortized issuance costs and discount on long-term debt		(0.4)	(0.6)
Long-term Debt		$ 236.6	373.7
5.586% - Capital Lease Obligations Due December 31, 2016 [Member] | NiSource Corporate Services [Member]
Interest rate on debt		5.586%
Capital lease obligations		$ 0	0.5
3.264% - Capital Lease Obligations Due October 31, 2019 [Member] | NiSource Corporate Services [Member]
Interest rate on debt		3.264%
Capital lease obligations		$ 1.9	2
2.156% - Capital Lease Obligations Due November 30, 2019 [Member] | NiSource Corporate Services [Member]
Interest rate on debt		2.156%
Capital lease obligations		$ 0.4	0
10.75% - Due March 15, 2016 [Member] | NiSource Finance Corporation [Member]
Interest rate on debt		10.75%
Long-Term Notes		$ 0	201.5
Variable Rate Due April 15, 2016 [Member] | NiSource Finance Corporation [Member]
Long-Term Notes		$ 0	325
5.41% - Due November 28, 2016 [Member] | NiSource Finance Corporation [Member]
Interest rate on debt		5.41%
Long-Term Notes		$ 0	90
Variable Rate Due August 18, 2017 [Member] | NiSource Finance Corporation [Member]
Long-Term Notes		$ 0	750
5.25% - Due September 15, 2017 [Member] | NiSource Finance Corporation [Member]
Interest rate on debt		5.25%
Long-Term Notes		$ 210.4	450
6.40% - Due March 15, 2018 [Member] | NiSource Finance Corporation [Member]
Interest rate on debt		6.40%
Long-Term Notes		$ 476	800
6.80% - Due January 15, 2019 [Member] | NiSource Finance Corporation [Member]
Interest rate on debt		6.80%
Long-Term Notes		$ 500	500
5.45% - Due September 15, 2020 [Member] | NiSource Finance Corporation [Member]
Interest rate on debt		5.45%
Long-Term Notes		$ 550	550
4.45% - Due December 1, 2021 [Member] | NiSource Finance Corporation [Member]
Interest rate on debt		4.45%
Long-Term Notes		$ 63.6	250
6.125% - Due March 1, 2022 [Member] | NiSource Finance Corporation [Member]
Interest rate on debt		6.125%
Long-Term Notes		$ 500	500
3.85% - Due February 15, 2023 [Member] | NiSource Finance Corporation [Member]
Interest rate on debt		3.85%
Long-Term Notes		$ 250	250
5.89% - Due November 28, 2025 [Member] | NiSource Finance Corporation [Member]
Interest rate on debt		5.89%
Long-Term Notes		$ 265	265
6.25% - Due December 15, 2040 [Member] | NiSource Finance Corporation [Member]
Interest rate on debt		6.25%
Long-Term Notes		$ 250	250
5.95% - Due June 15, 2041 [Member] | NiSource Finance Corporation [Member]
Interest rate on debt		5.95%
Long-Term Notes		$ 400	400
5.80% - Due February 1, 2042 [Member] | NiSource Finance Corporation [Member]
Interest rate on debt		5.80%
Long-Term Notes		$ 250	250
5.25% - Due February 15, 2043 [Member] | NiSource Finance Corporation [Member]
Interest rate on debt		5.25%
Long-Term Notes		$ 500	500
4.80% - Due February 15, 2044 [Member] | NiSource Finance Corporation [Member]
Interest rate on debt		4.80%
Long-Term Notes		$ 750	750
5.65% - Due February 1, 2045 [Member] | NiSource Finance Corporation [Member]
Interest rate on debt		5.65%
Long-Term Notes		$ 500	500
Pollution Control Bonds [Member] | NIPSCO [Member]
Long-Term Notes		$ 96	$ 226
[1]	This amount excludes $45.5 million of unamortized discount, premium and expenses.

Statements Of Consolidated Lon9

Statements Of Consolidated Long-Term Debt (Parenthetical) $ in Millions	12 Months Ended
	Dec. 31, 2015USD ($)
NIPSCO [Member]
Capital Lease Obligations	$ 45.5
Medium-Term Notes [Member] | Columbia Of Massachusetts [Member]
Minimum interest rate on debt	6.26%
Maximum interest rate on debt	6.43%
Weighted average interest rate on debt	6.30%
Medium-Term Notes [Member] | NiSource Capital Markets Inc [Member]
Minimum interest rate on debt	7.82%
Maximum interest rate on debt	7.99%
Weighted average interest rate on debt	7.92%
Medium-Term Notes [Member] | NIPSCO [Member]
Minimum interest rate on debt	7.02%
Maximum interest rate on debt	7.69%
Weighted average interest rate on debt	7.57%
Senior Notes [Member] | NiSource Capital Markets Inc [Member]
Interest rate on debt	6.78%
Debt Instrument, Maturity Date	Dec. 1, 2027
10.75% - Due March 15, 2016 [Member] | NiSource Finance Corporation [Member]
Interest rate on debt	10.75%
Debt Instrument, Maturity Date	Mar. 15, 2016
5.586% - Capital Lease Obligations Due December 31, 2016 [Member] | NiSource Corporate Services [Member]
Capital Lease Obligations	$ 0
Interest rate on debt	5.586%
Debt Instrument, Maturity Date	Dec. 31, 2016
3.264% - Capital Lease Obligations Due October 31, 2019 [Member] | NiSource Corporate Services [Member]
Capital Lease Obligations	$ 1.9
Interest rate on debt	3.264%
Debt Instrument, Maturity Date	Oct. 31, 2019
2.156% - Capital Lease Obligations Due November 30, 2019 [Member] | NiSource Corporate Services [Member]
Capital Lease Obligations	$ 0.4
Interest rate on debt	2.156%
Debt Instrument, Maturity Date	Nov. 30, 2019
Notes Payable, Other Payables [Member] | NiSource Development Company Inc [Member]
Interest rate on debt	5.56%
Debt Instrument, Maturity Date	Jul. 1, 2041
Variable Rate Due April 15, 2016 [Member] | NiSource Finance Corporation [Member]
Interest rate on debt	1.17%
Debt Instrument, Maturity Date	Apr. 15, 2016
5.41% - Due November 28, 2016 [Member] | NiSource Finance Corporation [Member]
Interest rate on debt	5.41%
Debt Instrument, Maturity Date	Nov. 28, 2016
Variable Rate Term Loan Due August Eighteenth Two Thousand Seventeen[Member] [Member] | NiSource Finance Corporation [Member]
Interest rate on debt	1.17%
Debt Instrument, Maturity Date	Aug. 18, 2017
5.25% - Due September 15, 2017 [Member] | NiSource Finance Corporation [Member]
Interest rate on debt	5.25%
Debt Instrument, Maturity Date	Sep. 15, 2017
6.40% - Due March 15, 2018 [Member] | NiSource Finance Corporation [Member]
Interest rate on debt	6.40%
Debt Instrument, Maturity Date	Mar. 15, 2018
6.80% - Due January 15, 2019 [Member] | NiSource Finance Corporation [Member]
Interest rate on debt	6.80%
Debt Instrument, Maturity Date	Jan. 15, 2019
5.45% - Due September 15, 2020 [Member] | NiSource Finance Corporation [Member]
Interest rate on debt	5.45%
Debt Instrument, Maturity Date	Sep. 15, 2020
4.45% - Due December 1, 2021 [Member] | NiSource Finance Corporation [Member]
Interest rate on debt	4.45%
Debt Instrument, Maturity Date	Dec. 1, 2021
6.125% - Due March 1, 2022 [Member] | NiSource Finance Corporation [Member]
Interest rate on debt	6.125%
Debt Instrument, Maturity Date	Mar. 1, 2022
3.85% - Due February 15, 2023 [Member] | NiSource Finance Corporation [Member]
Interest rate on debt	3.85%
Debt Instrument, Maturity Date	Feb. 15, 2023
5.89% - Due November 28, 2025 [Member] | NiSource Finance Corporation [Member]
Interest rate on debt	5.89%
Debt Instrument, Maturity Date	Nov. 28, 2025
6.25% - Due December 15, 2040 [Member] | NiSource Finance Corporation [Member]
Interest rate on debt	6.25%
Debt Instrument, Maturity Date	Dec. 15, 2040
5.95% - Due June 15, 2041 [Member] | NiSource Finance Corporation [Member]
Interest rate on debt	5.95%
Debt Instrument, Maturity Date	Jun. 15, 2041
5.80% - Due February 1, 2042 [Member] | NiSource Finance Corporation [Member]
Interest rate on debt	5.80%
Debt Instrument, Maturity Date	Feb. 1, 2042
5.25% - Due February 15, 2043 [Member] | NiSource Finance Corporation [Member]
Interest rate on debt	5.25%
Debt Instrument, Maturity Date	Feb. 15, 2043
4.80% - Due February 15, 2044 [Member] | NiSource Finance Corporation [Member]
Interest rate on debt	4.80%
Debt Instrument, Maturity Date	Feb. 15, 2044
5.65% - Due February 1, 2045 [Member] | NiSource Finance Corporation [Member]
Interest rate on debt	5.65%
Debt Instrument, Maturity Date	Feb. 1, 2045
Pollution Control Bonds [Member] | NIPSCO [Member]
Minimum interest rate on debt	5.70%
Maximum interest rate on debt	5.85%
Weighted average interest rate on debt	5.76%
Capital Lease Obligations [Member] | NIPSCO [Member]
Interest rate on debt	3.95%
Debt Instrument, Maturity Date	Jun. 30, 2022
Minimum [Member] | Medium-Term Notes [Member] | Columbia Of Massachusetts [Member]
Debt Instrument, Maturity Date	Dec. 15, 2025
Minimum [Member] | Medium-Term Notes [Member] | NiSource Capital Markets Inc [Member]
Debt Instrument, Maturity Date	Mar. 27, 2017
Minimum [Member] | Medium-Term Notes [Member] | NIPSCO [Member]
Debt Instrument, Maturity Date	Jun. 12, 2017
Minimum [Member] | Pollution Control Bonds [Member] | NIPSCO [Member]
Debt Instrument, Maturity Date	Jul. 1, 2017
Maximum [Member] | Medium-Term Notes [Member] | Columbia Of Massachusetts [Member]
Debt Instrument, Maturity Date	Feb. 15, 2028
Maximum [Member] | Medium-Term Notes [Member] | NiSource Capital Markets Inc [Member]
Debt Instrument, Maturity Date	May 5, 2027
Maximum [Member] | Medium-Term Notes [Member] | NIPSCO [Member]
Debt Instrument, Maturity Date	Aug. 4, 2027
Maximum [Member] | Pollution Control Bonds [Member] | NIPSCO [Member]
Debt Instrument, Maturity Date	Apr. 1, 2019

Statements Of Consolidated Comm

Statements Of Consolidated Common Stockholders' Equity - USD ($) $ in Millions		Total	Common Stock [Member]	Treasury Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Beginning Balance at Dec. 31, 2012		$ 5,554.3	$ 3.1	$ (40.5)	$ 4,597.6	$ 1,059.6	$ (65.5)
Comprehensive Income (Loss):
Net Income		532.1	0	0	0	532.1	0
Other comprehensive income (loss), net of tax		21.9	0	0	0	0	21.9
Dividends:
Common stock		(306.2)	0	0	0	(306.2)	0
Treasury stock acquired		(8.1)	0	(8.1)	0	0	0
Issued:
Stock Issued During Period, Value, New Issues		0.1	0.1	0	0	0	0
Employee stock purchase plan		2.9	0	0	2.9	0	0
Long-term incentive plan		43.8	0	0	43.8	0	0
401(k) and profit sharing issuance		37.8	0	0	37.8	0	0
Dividend reinvestment plan		8	0	0	8	0	0
Ending Balance at Dec. 31, 2013		5,886.6	3.2	(48.6)	4,690.1	1,285.5	(43.6)
Comprehensive Income (Loss):
Net Income		530	0	0	0	530	0
Other comprehensive income (loss), net of tax		(7)	0	0	0	0	(7)
Dividends:
Common stock		(321.5)	0	0	0	(321.5)	0
Treasury stock acquired		(10.3)	0	(10.3)	0	0	0
Issued:
Employee stock purchase plan		4.2	0	0	4.2	0	0
Long-term incentive plan		40.2	0	0	40.2	0	0
401(k) and profit sharing issuance		45.3	0	0	45.3	0	0
Dividend reinvestment plan		7.8	0	0	7.8	0	0
Ending Balance at Dec. 31, 2014		6,175.3	3.2	(58.9)	4,787.6	1,494	(50.6)
Comprehensive Income (Loss):
Net Income		286.5	0	0	0	286.5	0
Other comprehensive income (loss), net of tax		(11)	0	0	0	0	(11)
Allocation of AOCI to Noncontrolling Interest	[1]	2	0	0	0	0	2
Dividends:
Common stock		(263.5)	0	0	0	(263.5)	0
Stockholders' Equity Note, Spinoff Transaction		(2,615.8)	0	0	0	(2,640.3)	24.5
Treasury stock acquired		(20.4)	0	(20.4)	0	0	0
Issued:
Employee stock purchase plan		5.1	0	0	5.1	0	0
Long-term incentive plan		4.2	0	0	4.2	0	0
401(k) and profit sharing issuance		46.7	0	0	46.7	0	0
Dividend reinvestment plan		7.3	0	0	7.3	0	0
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders	[1],[2]	227.1	0	0	227.1	0	0
Ending Balance at Dec. 31, 2015		$ 3,843.5	$ 3.2	$ (79.3)	$ 5,078	$ (1,123.3)	$ (35.1)
[1]	This transaction, which occurred prior to the Separation, was distributed through retained earnings as part of the Separation on July 1, 2015.
[2]	Represents the purchase of an additional 8.4% limited partner interest in Columbia OpCo by an affiliate of CPG, recorded at the historical carrying value of Columbia OpCo's net assets after giving effect to the $1,168.4 million equity contribution from CPPL's IPO completed on February 11, 2015.

Statements Of Consolidated Co11

Statements Of Consolidated Common Stockholders' Equity (Shares) (Parenthetical) - USD ($) shares in Thousands, $ in Millions	Feb. 11, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Beginning Balance, shares		316,037	313,676	310,281
Shares
Treasury stock acquired, shares		(472)	(292)	(297)
Issued:
Employee stock purchase plan, shares		203	113	102
Long-term incentive plan, shares		1,423	1,125	2,037
Dividend reinvestment, shares		275	206	272
Retirement Savings Plan		1,644	1,209	1,281
Ending Balance, shares		319,110	316,037	313,676
Proceeds from Issuance Initial Public Offering	$ 1,168.4
Limited Liability Company (LLC) or Limited Partnership (LP), Members or Limited Partners, Ownership Interest		8.40%
Common Stock, Dividends, Per Share, Declared		$ 0.83	$ 1.02	$ 0.98
Common Stock [Member]
Beginning Balance, shares		318,636	315,983	312,291
Issued:
Employee stock purchase plan, shares		203	113	102
Long-term incentive plan, shares		1,423	1,125	2,037
Dividend reinvestment, shares		275	206	272
Retirement Savings Plan		1,644	1,209	1,281
Ending Balance, shares		322,181	318,636	315,983
Treasury Stock [Member]
Beginning Balance, shares		(2,599)	(2,307)	(2,010)
Shares
Treasury stock acquired, shares		(472)	(292)	(297)
Issued:
Employee stock purchase plan, shares		0	0	0
Long-term incentive plan, shares		0	0	0
Dividend reinvestment, shares		0	0	0
Retirement Savings Plan		0	0	0
Ending Balance, shares		(3,071)	(2,599)	(2,307)

Nature of Operations And Summar

Nature of Operations And Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2015
Nature of Operations And Summary of Significant Accounting Policies [Abstract]
Significant Accounting Policies [Text Block]	Nature of Operations and Summary of Significant Accounting Policies A. Company Structure and Principles of Consolidation . NiSource, a Delaware corporation, is an energy holding company whose subsidiaries are fully regulated natural gas and electric utility companies serving approximately 3.9 million customers in seven states. NiSource generates substantially all of its operating income through these rate-regulated businesses. The consolidated financial statements include the accounts of NiSource and its majority-owned subsidiaries after the elimination of all intercompany accounts and transactions. Investments for which at least a 20% interest is owned, certain joint ventures and limited partnership interests of more than 3% are accounted for under the equity method. Except where noted above and in the event where NiSource has significant influence, investments with less than a 20% interest are accounted for under the cost method. NiSource also consolidates variable interest entities for which NiSource is the primary beneficiary. On July 1, 2015, NiSource completed the Separation. CPG's operations consisted of all of NiSource's Columbia Pipeline Group Operations segment prior to the Separation. Following the Separation, NiSource retained no ownership interest in CPG. The results of operations and cash flows for the former Columbia Pipeline Group Operations segment have been reported as discontinued operations for all periods presented. Additionally, the assets and liabilities of the former Columbia Pipeline Group Operations segment were reclassified as assets and liabilities of discontinued operations for all prior periods. See Note 3, "Discontinued Operations," for additional information. B. Use of Estimates. The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements, and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. C. Cash, Cash Equivalents, and Restricted Cash . NiSource considers all investments with original maturities of three months or less to be cash equivalents. NiSource reports amounts deposited in brokerage accounts for margin requirements as restricted cash. In addition, NiSource has amounts deposited in trust to satisfy requirements for the provision of various property, liability, workers compensation, and long-term disability insurance, which is classified as restricted cash and disclosed as an investing cash flow on the Statements of Consolidated Cash Flows. Restricted cash was $ 29.7 million and $ 24.9 million as of December 31, 2015 and 2014 , respectively. The increase in restricted cash was primarily a result of higher margin requirements due to open derivative contracts. D. Accounts Receivable and Unbilled Revenue. Accounts receivable on the Consolidated Balance Sheets includes both billed and unbilled amounts as NiSource believes that total accounts receivable is a more meaningful presentation, given the factors which impact both billed and unbilled accounts receivable. Unbilled revenue is based on estimated amounts of electric energy or natural gas delivered but not yet billed to its customers. Unbilled amounts of accounts receivable relate to a portion of a customer’s consumption of gas or electricity from the date of the last cycle billing date through the last day of the month (balance sheet date). Factors taken into consideration when estimating unbilled revenue include historical usage, customer rates and weather. Accounts receivable fluctuates from year to year depending in large part on weather impacts and price volatility. NiSource’s accounts receivable on the Consolidated Balance Sheets includes unbilled revenue, less reserves, in the amounts of $237.1 million and $340.5 million for the years ended December 31, 2015 and 2014 , respectively. The reserve for uncollectible receivables is the Company’s best estimate of the amount of probable credit losses in the existing accounts receivable. The Company determined the reserve based on historical experience and in consideration of current market conditions. Account balances are charged against the allowance when it is anticipated the receivable will not be recovered. E. Investments in Debt and Equity Securities. NiSource’s investments in debt and equity securities are carried at fair value and are designated as available-for-sale. These investments are included within “Other investments” on the Consolidated Balance Sheets. Unrealized gains and losses, net of deferred income taxes, are reflected as accumulated other comprehensive income (loss). These investments are monitored for other than temporary declines in market value. Realized gains and losses and permanent impairments are reflected in the Statements of Consolidated Income. No material impairment charges were recorded for the years ended December 31, 2015 , 2014 and 2013 . F. Basis of Accounting for Rate-Regulated Subsidiaries . Rate-regulated subsidiaries account for and report assets and liabilities consistent with the economic effect of the way in which regulators establish rates, if the rates established are designed to recover the costs of providing the regulated service and it is probable that such rates can be charged and collected. Certain expenses and credits subject to utility regulation or rate determination normally reflected in income are deferred on the Consolidated Balance Sheets and are recognized in income as the related amounts are included in customer rates and recovered from or refunded to customers. In the event that regulation significantly changes the opportunity for NiSource to recover its costs in the future, all or a portion of NiSource’s regulated operations may no longer meet the criteria for regulatory accounting. In such an event, a write-down of all or a portion of NiSource’s existing regulatory assets and liabilities could result. If transition cost recovery was approved by the appropriate regulatory bodies that would meet the requirements under GAAP for continued accounting as regulatory assets and liabilities during such recovery period, the regulatory assets and liabilities would be reported at the recoverable amounts. If unable to continue to apply the provisions of regulatory accounting, NiSource would be required to apply the provisions of ASC 980-20, Discontinuation of Rate-Regulated Accounting . In management’s opinion, NiSource’s regulated subsidiaries will be subject to regulatory accounting for the foreseeable future. Refer to Note 7, "Regulatory Matters," for additional information. G. Utility Plant and Other Property and Related Depreciation and Maintenance . Property, plant and equipment (principally utility plant) is stated at cost. The rate-regulated subsidiaries record depreciation using composite rates on a straight-line basis over the remaining service lives of the electric, gas and common properties as approved by the appropriate regulators. The weighted average depreciation provisions for utility plant, as a percentage of the original cost, for the periods ended December 31, 2015 , 2014 and 2013 were as follows: 2015 2014 2013 Electric Operations 3.1 % 3.0 % 3.2 % Gas Distribution Operations 2.0 % 2.1 % 2.1 % For rate-regulated companies, AFUDC is capitalized on all classes of property except organization costs, land, autos, office equipment, tools and other general property purchases. The allowance is applied to construction costs for that period of time between the date of the expenditure and the date on which such project is placed in service. The pre-tax rate for AFUDC was 4.7% in 2015 , 4.5% in 2014 and 4.1% in 2013 . Generally, NiSource’s subsidiaries follow the practice of charging maintenance and repairs, including the cost of removal of minor items of property, to expense as incurred. When regulated property that represents a retired unit is replaced or removed, the cost of such property is credited to utility plant, and such cost, net of salvage, is charged to the accumulated provision for depreciation in accordance with composite depreciation. H. Carrying Charges and Deferred Depreciation. NIPSCO has capitalized debt-based carrying charges and deferred depreciation related to Sugar Creek in accordance with the February 18, 2008 Order of the IURC. The deferral of Sugar Creek debt-based carrying charges and the deferral of depreciation ceased in December 2011 and deferred balances are being amortized over five years beginning January 2012. As of December 31, 2015 , the remaining balance to be amortized is $14.3 million . An additional $13.9 million is deferred for consideration in NIPSCO's current electric base rate case. Management believes this amount is probable of recovery through future rates. In 2005, the PUCO authorized Columbia of Ohio to revise its depreciation accrual rates for the period beginning January 1, 2005. The revised depreciation rates are now higher than those which would have been utilized if Columbia of Ohio were not subject to regulation. The amount of depreciation that would have been recorded for 2005 through 2015 had Columbia of Ohio not been subject to rate regulation is a combined $559.8 million , $66.4 million less than the $626.2 million reflected in rates. The regulatory asset was $65.3 million and $72.3 million as of December 31, 2015 and 2014 , respectively. The amount of depreciation that would have been recorded for 2015 had Columbia of Ohio not been subject to rate regulation is $74.7 million , $7.0 million less than the $81.7 million reflected in rates. Columbia of Ohio has PUCO approval to defer depreciation associated with its IRP and capital expenditure program. As of December 31, 2015, depreciation of $38.5 million was deferred for the programs. Recovery of the IRP depreciation is approved annually through the IRP rider (see Note 7, "Regulatory Matters"). The equivalent of annual depreciation expense, based on the average life of the related assets, is included in the calculation of the rider approved by the PUCO and billed to customers. Deferred depreciation expense is recognized as the rider is billed to customers. The recovery mechanism for depreciation associated with the capital expenditure program will be addressed in a separate proceeding. I. Amortization of Software Costs. External and internal costs associated with computer software developed for internal use are capitalized. Capitalization of such costs commences upon the completion of the preliminary stage of each project. Once the installed software is ready for its intended use, such capitalized costs are amortized on a straight-line basis generally over a period of five years. NiSource amortized $41.1 million in 2015 , $33.7 million in 2014 and $31.3 million in 2013 related to software costs. NiSource’s unamortized software balance was $167.1 million and $162.3 million at December 31, 2015 and 2014 , respectively. J. Goodwill and Other Intangible Assets. NiSource has $1,690.7 million in goodwill. Substantially all goodwill relates to the excess of cost over the fair value of the net assets acquired in the Columbia acquisition on November 1, 2000. In addition, NiSource has other intangible assets consisting primarily of franchise rights apart from goodwill that were identified as part of the purchase price allocations associated with the acquisition of Columbia of Massachusetts, a wholly-owned subsidiary of NiSource, which is being amortized on a straight-line basis over forty years from the date of acquisition. See Note 5, "Goodwill and Other Intangible Assets," for additional information. K. Long-lived Assets. NiSource’s Consolidated Balance Sheets contain significant long-lived assets other than goodwill and intangible assets discussed above. As a result, NiSource assesses the carrying amount and potential earnings of these assets whenever events or changes in circumstances indicate that the carrying value could be impaired. There were no significant impairments for the years ended December 31, 2015, 2014 and 2013. L. Revenue Recognition. Revenue is recorded as products and services are delivered. Utility revenues are billed to customers monthly on a cycle basis. Revenues are recorded on the accrual basis and include estimates for electricity and gas delivered but not billed. M. Earnings Per Share. Basic EPS is computed by dividing net income attributable to NiSource by the weighted-average number of shares of common stock outstanding for the period. The weighted average shares outstanding for diluted EPS include the incremental effects of the various long-term incentive compensation plans. The numerator in calculating both basic and diluted EPS for each year is reported net income attributable to NiSource. The computation of diluted average common shares follows: Diluted Average Common Shares Computation 2015 2014 2013 Denominator (thousands) Basic average common shares outstanding 317,746 315,120 312,402 Dilutive potential common shares Nonqualified stock options — 6 80 Shares contingently issuable under employee stock plans (1) — 1,066 708 Shares restricted under stock plans (1) 2,090 444 456 Diluted Average Common Shares 319,836 316,636 313,646 (1) Change due to Separation-related adjustments, see Note 13, "Share-Based Compensation." N. Estimated Rate Refunds . Certain rate-regulated subsidiaries collect revenues subject to refund pending final determination in rate proceedings. In connection with such revenues, estimated rate refund liabilities are recorded which reflect management’s current judgment of the ultimate outcomes of the proceedings. No provisions are made when, in the opinion of management, the facts and circumstances preclude a reasonable estimate of the outcome. O. Accounts Receivable Transfer Program. Certain of NiSource’s subsidiaries have agreements with third parties to sell certain accounts receivable without recourse. These transfers of accounts receivable are accounted for as secured borrowings. The entire gross receivables balance remains on the December 31, 2015 and 2014 Consolidated Balance Sheets and short-term debt is recorded in the amount of proceeds received from the purchasers involved in the transactions. Fees associated with the securitization transactions are recorded as interest expense. Refer to Note 17, "Transfers of Financial Assets," for further information. P. Fuel Adjustment Clause. NIPSCO defers most differences between fuel and power purchase costs and the recovery of such costs in revenue, and adjusts future billings for such deferrals on a basis consistent with applicable state-approved tariff provisions. Q. Gas Cost Adjustment Clause. All of NiSource’s Gas Distribution Operations subsidiaries defer most differences between gas purchase costs and the recovery of such costs in revenues, and adjust future billings for such deferrals on a basis consistent with applicable state-approved tariff provisions. R. Gas Inventory. Both the LIFO inventory methodology and the weighted average cost methodology are used to value natural gas in storage, as approved by regulators for each of NiSource’s regulated subsidiaries. Inventory valued using LIFO was $50.2 million and $55.1 million at December 31, 2015 , and 2014 , respectively. Based on the average cost of gas using the LIFO method, the estimated replacement cost of gas in storage was less than the stated LIFO cost by $27.2 million and $15.8 million at December 31, 2015 and 2014 , respectively. Inventory valued using the weighted average cost methodology was $293.3 million at December 31, 2015 and $385.2 million at December 31, 2014 . S. Accounting for Exchange and Balancing Arrangements of Natural Gas. NiSource’s Gas Distribution Operations segment enters into balancing and exchange arrangements of natural gas as part of its operations and off-system sales programs. NiSource records a receivable or payable for its respective cumulative gas imbalances as well as for any gas inventory borrowed or lent under a Gas Distributions Operations exchange agreement. These receivables and payables are recorded as “Exchange gas receivable” or “Exchange gas payable” on NiSource’s Consolidated Balance Sheets, as appropriate. T. Accounting for Risk Management Activities. NiSource accounts for its derivatives and hedging activities in accordance with ASC 815. NiSource recognizes all derivatives as either assets or liabilities on the Consolidated Balance Sheets at fair value, unless such contracts are exempted as a normal purchase normal sale under the provisions of the standard. The accounting for changes in the fair value of a derivative depends on the intended use of the derivative and resulting designation. There were no material derivative assets or liabilities as of December 31, 2015 and 2014. U. Income Taxes and Investment Tax Credits. NiSource records income taxes to recognize full interperiod tax allocations. Under the liability method, deferred income taxes are provided for the tax consequences of temporary differences by applying enacted statutory tax rates applicable to future years to differences between the financial statement carrying amount and the tax basis of existing assets and liabilities. Previously recorded investment tax credits of the regulated subsidiaries were deferred on the balance sheet and are being amortized to book income over the regulatory life of the related properties to conform to regulatory policy. To the extent certain deferred income taxes of the regulated companies are recoverable or payable through future rates, regulatory assets and liabilities have been established. Regulatory assets for income taxes are primarily attributable to property related tax timing differences for which deferred taxes had not been provided in the past, when regulators did not recognize such taxes as costs in the ratemaking process. Regulatory liabilities for income taxes are primarily attributable to the regulated companies’ obligation to refund to ratepayers deferred income taxes provided at rates higher than the current federal income tax rate. Such amounts are credited to ratepayers using either the average rate assumption method or the reverse South Georgia method. Pursuant to the U.S. Internal Revenue Code and relevant state taxing authorities, NiSource and its subsidiaries file consolidated income tax returns for federal and certain state jurisdictions. NiSource and its subsidiaries are parties to an agreement (the “Tax Allocation Agreement”) that provides for the allocation of consolidated tax liabilities. The Tax Allocation Agreement generally provides that each party is allocated an amount of tax similar to that which would be owed had the party been separately subject to tax. On June 30, 2015, in connection with the Separation, NiSource entered into an additional Tax Allocation Agreement with CPG to set forth their agreement with respect to tax matters for taxable periods prior to and including June 30, 2015. V. Environmental Expenditures. NiSource accrues for costs associated with environmental remediation obligations when the incurrence of such costs is probable and the amounts can be reasonably estimated, regardless of when the expenditures are actually made. The undiscounted estimated future expenditures are based on currently enacted laws and regulations, existing technology and estimated site-specific costs where assumptions may be made about the nature and extent of site contamination, the extent of cleanup efforts, costs of alternative cleanup methods and other variables. The liability is adjusted as further information is discovered or circumstances change. The reserves for estimated environmental expenditures are recorded on the Consolidated Balance Sheets in “Legal and environmental” reserves for short-term portions of these liabilities and “Other noncurrent liabilities” for the respective long-term portions of these liabilities. Rate-regulated subsidiaries applying regulatory accounting establish regulatory assets on the Consolidated Balance Sheets to the extent that future recovery of environmental remediation costs is probable through the regulatory process. Refer to Note 18, "Other Commitments and Contingencies," for further information. W. Excise Taxes. NiSource accounts for excise taxes that are customer liabilities by separately stating on its invoices the tax to its customers and recording amounts invoiced as liabilities payable to the applicable taxing jurisdiction. These types of taxes, comprised largely of sales taxes collected, are presented on a net basis affecting neither revenues nor cost of sales. NiSource accounts for taxes for which it is liable by recording a liability for the expected tax with a corresponding charge to “Other taxes” expense.

Recent Accounting Pronouncement

Recent Accounting Pronouncements	12 Months Ended
	Dec. 31, 2015
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Recent Accounting Pronouncements	Recent Accounting Pronouncements In January 2016, the FASB issued ASU 2016-01, Recognition and Measurement of Financial Assets and Financial Liabilities. ASU 2016-01 makes limited amendments to the guidance in GAAP on the classification and measurement of financial instruments. The standard requires entities to measure equity investments that do not result in consolidation and are not accounted for under the equity method at fair value and recognize any changes in fair value in net income unless the investments qualify for the new practicability exception. Additionally, entities will have to record changes in instrument-specific credit risk for financial liabilities measured under the fair value option in other comprehensive income. NiSource is required to adopt ASU 2016-01 for periods beginning after December 15, 2017, including interim periods, with early adoption permitted for certain aspects of the standard. NiSource is currently evaluating the impact the adoption of ASU 2016-01 will have on its Consolidated Financial Statements or Notes to Consolidated Financial Statements. In November 2015, the FASB issued ASU 2015-17, Income Taxes (Topic 740): Balance Sheet Classification of Deferred Taxes . ASU 2015-17 requires entities to present deferred tax assets and liabilities as noncurrent on the balance sheet. This ASU simplifies current guidance which requires entities to separately classify deferred tax assets and liabilities as current or noncurrent on the balance sheet. NiSource is required to adopt ASU 2015-17 for periods beginning after December 15, 2016, including interim periods, with early adoption permitted. NiSource adopted ASU 2015-17 as of December 31, 2015 for both current and prior periods. See Note 9, "Income Taxes," in the Notes to Consolidated Financial Statements for more information on the impact of adopting this standard. In July 2015, the FASB issued ASU 2015-11, Inventory (Topic 330): Simplifying the Measurement of Inventory . ASU 2015-11 replaces the current lower of cost or market test with a lower of cost or net realizable value test. The new standard applies only to inventories for which cost is determined by methods other than LIFO and the retail inventory method. NiSource is required to adopt ASU 2015-11 for periods beginning after December 15, 2016, including interim periods, with early adoption permitted. NiSource is currently evaluating the impact the adoption of ASU 2015-11 will have on the Consolidated Financial Statements or Notes to Consolidated Financial Statements. In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606) . ASU 2014-09 outlines a single, comprehensive model for entities to use in accounting for revenue arising from contracts with customers and supersedes most current revenue recognition guidance. The core principle of the new standard is that an entity should recognize revenue to depict the transfer of goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. In July 2015, the FASB deferred the effective date by one year for ASU 2014-09 to annual reporting periods beginning after December 15, 2017, including interim periods. Companies are permitted to adopt ASU 2014-09 on the original effective date of the ASU. NiSource is currently evaluating the impact the adoption of ASU 2014-09 will have on its Consolidated Financial Statements or Notes to Consolidated Financial Statements. In April 2015, the FASB issued ASU 2015-07, Disclosures for Investments in Certain Entities that Calculate Net Asset Value (NAV) per Share (or its Equivalent) . ASU 2015-07 eliminates the requirement to categorize investments measured at NAV in the fair value hierarchy table. Instead, an entity is required to include those investments as a reconciling line item so that the total fair value of investments in the footnote disclosure reconciles to the Consolidated Balance Sheets. NiSource is required to adopt ASU 2015-07 for periods beginning after December 15, 2015, including interim periods, and the guidance is to be applied retrospectively, with early adoption permitted. NiSource adopted ASU 2015-07 as of December 31, 2015. The adoption of this guidance did not have a material impact on the Consolidated Financial Statements or Notes to Consolidated Financial Statements. In April 2015, the FASB issued ASU 2015-05, Intangibles - Goodwill and Other-Internal-Use Software (Subtopic 350-40): Customer's Accounting for Fees Paid in a Cloud Computing Arrangement. ASU 2015-05 clarifies guidance on determining whether a cloud computing arrangement contains a software license that should be accounted for as internal-use software. NiSource is required to adopt ASU 2015-05 for periods beginning after December 15, 2015, including interim periods, and the guidance is permitted to be applied either (1) prospectively to all agreements entered into or materially modified after the effective date or (2) retrospectively, with early adoption permitted. NiSource is currently evaluating the impact the adoption of ASU 2015-05 will have on the Consolidated Financial Statements or Notes to Consolidated Financial Statements. In April 2015, the FASB issued ASU 2015-03, Interest - Imputation of Interest (Subtopic 835-30) : Simplifying the Presentation of Debt Issuance Costs . ASU 2015-03 changes the way entities present debt issuance costs in financial statements by presenting issuance costs on the balance sheet as a direct deduction from the related debt liability rather than as a deferred charge. Amortization of these costs will continue to be reported as interest expense. NiSource is required to adopt ASU 2015-03 for periods beginning after December 15, 2015, including interim periods, and the guidance is to be applied retrospectively with early adoption permitted. NiSource adopted ASU 2015-03 as of December 31, 2015. The adoption of this standard did not have a material impact on the Consolidated Financial Statements or Notes to Consolidated Financial Statements.

Discontinued Operations

Discontinued Operations	12 Months Ended
	Dec. 31, 2015
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Discontinued Operations And Assets And Liabilities Held For Sale	On July 1, 2015, NiSource completed the Separation through a special pro rata stock dividend, distributing one share of CPG common stock for every one share of NiSource common stock held by any NiSource stockholder on June 19, 2015, the record date. The Separation resulted in two stand-alone energy infrastructure companies: NiSource, a fully regulated natural gas and electric utilities company, and CPG, a natural gas pipeline, midstream and storage company. As a stand-alone company, on the date of the Separation, CPG's operations consisted of NiSource's Columbia Pipeline Group Operations segment prior to the Separation. Following the Separation, NiSource retained no ownership interest in CPG. On the date of the Separation, CPG consisted of approximately $9.2 billion of assets, $5.6 billion of liabilities and $3.6 billion of equity. The results of operations and cash flows for the former Columbia Pipeline Group Operations segment have been reported as discontinued operations for all periods presented. Additionally, the assets and liabilities of the former Columbia Pipeline Group Operations segment were reclassified as assets and liabilities of discontinued operations for all prior periods. On September 1, 2013, NiSource sold the commercial and industrial natural gas portfolio of its unregulated natural gas marketing business. The sale included the physical contracts and associated financial hedges that comprise the portfolio, as well as the gas inventory and customer deposits of the business. For the year ended December 31, 2013, an after tax loss of $1.5 million was included in Gain on Disposition of Discontinued Operations, net of taxes in the Statements of Consolidated Income. In January 2013, NiSource sold the service plan and leasing business lines of its Retail Services business. For the year ended December 31, 2013, an after tax gain of $36.4 million was included in Gain on Disposition of Discontinued Operations, net of taxes in the Statements of Consolidated Income. Results from discontinued operations are provided in the following table. These results are primarily from NiSource's former Columbia Pipeline Group Operations segment. Year Ended December 31, 2015 (in millions) Columbia Pipeline Group Operations Corporate and Other Total Net Revenues Transportation and storage revenues $ 561.4 $ — $ 561.4 Other revenues 94.3 — 94.3 Total Sales Revenues 655.7 — 655.7 Less: Cost of sales (excluding depreciation and amortization) 0.2 — 0.2 Net Revenues 655.5 — 655.5 Operating Expenses Operation and maintenance 375.8 (1) — 375.8 Depreciation and amortization 66.4 — 66.4 Gain on sale of assets (13.6 ) — (13.6 ) Other taxes 38.0 — 38.0 Total Operating Expenses 466.6 — 466.6 Equity Earnings in Unconsolidated Affiliates 29.1 — 29.1 Operating Income from Discontinued Operations 218.0 — 218.0 Other Income (Deductions) Interest expense, net (37.1 ) — (37.1 ) Other, net 7.8 0.4 8.2 Total Other Income (Deductions) (29.3 ) 0.4 (28.9 ) Income from Discontinued Operations before Income Taxes 188.7 0.4 189.1 Income Taxes 84.7 0.9 85.6 Income (Loss) from Discontinued Operations - net of taxes $ 104.0 $ (0.5 ) $ 103.5 (1) Includes approximately $55.4 million of transaction costs related to the Separation. Year Ended December 31, 2014 (in millions) Columbia Pipeline Group Operations Corporate and Other Total Net Revenues Transportation and storage revenues $ 1,034.3 $ — $ 1,034.3 Other revenues 312.9 — 312.9 Total Sales Revenues 1,347.2 — 1,347.2 Less: Cost of sales (excluding depreciation and amortization) 0.3 — 0.3 Net Revenues 1,346.9 — 1,346.9 Operating Expenses Operation and maintenance 769.1 (1) — 769.1 Depreciation and amortization 118.6 — 118.6 Gain on sale of assets (34.5 ) — (34.5 ) Other taxes 67.1 — 67.1 Total Operating Expenses 920.3 — 920.3 Equity Earnings in Unconsolidated Affiliates 46.6 — 46.6 Operating Income from Discontinued Operations 473.2 — 473.2 Other Income (Deductions) Interest expense, net (64.1 ) — (64.1 ) Other, net 8.9 (1.0 ) 7.9 Total Other Income (Deductions) (55.2 ) (1.0 ) (56.2 ) Income (Loss) from Discontinued Operations before Income Taxes 418.0 (1.0 ) 417.0 Income Taxes 143.5 (0.3 ) 143.2 Income (Loss) from Discontinued Operations - net of taxes $ 274.5 $ (0.7 ) $ 273.8 (1) Includes approximately $23.7 million of transaction costs related to the Separation. Year Ended December 31, 2013 (in millions) Columbia Pipeline Group Operations Corporate and Other Total Net Revenues Transportation and storage revenues $ 971.1 $ — $ 971.1 Other revenues 208.7 2.5 211.2 Total Sales Revenues 1,179.8 2.5 1,182.3 Less: Cost of sales (excluding depreciation and amortization) 0.4 — 0.4 Net Revenues 1,179.4 2.5 1,181.9 Operating Expenses Operation and maintenance 619.5 — 619.5 Depreciation and amortization 106.9 — 106.9 Gain on sale of assets (18.6 ) — (18.6 ) Other taxes 62.2 — 62.2 Total Operating Expenses 770.0 — 770.0 Equity Earnings in Unconsolidated Affiliates 35.9 — 35.9 Operating Income from Discontinued Operations 445.3 2.5 447.8 Other Income (Deductions) Interest expense, net (39.5 ) — (39.5 ) Other, net 17.4 9.1 26.5 Total Other Income (Deductions) (22.1 ) 9.1 (13.0 ) Income from Discontinued Operations before Income Taxes 423.2 11.6 434.8 Income Taxes 153.3 5.3 158.6 Income from Discontinued Operations - net of taxes $ 269.9 $ 6.3 $ 276.2 Gain on Disposition of Discontinued Operations - net of taxes $ — $ 34.9 $ 34.9 CPG’s financing requirements prior to the private placement of senior notes on May 22, 2015 were satisfied through borrowings from NiSource Finance. Interest expense from discontinued operations primarily represents net interest charged to CPG from NiSource Finance, less AFUDC. Subsequent to May 22, 2015, interest expense from discontinued operations also includes interest incurred on CPG’s private placement of $2,750.0 million of senior notes. Continuing Involvement Natural gas transportation and storage services provided to NiSource by CPG were $147.6 million , $146.2 million and $147.6 million for the years ended December 31, 2015, 2014 and 2013, respectively. Prior to July 1, 2015, these costs were eliminated in consolidation. Beginning July 1, 2015, these costs and associated cash flows represent third-party transactions with CPG and are not eliminated in consolidation, as such services have continued subsequent to the Separation and are expected to continue for the foreseeable future. As a result of the Separation, NiSource and CPG entered into Transition Services Agreements (TSAs). NiSource expects the TSAs to terminate within 18 months from the date of the Separation. The TSAs set forth the terms and conditions for NiSource and CPG to provide certain transition services to one another. Under the TSAs, NiSource provides CPG certain information technology, financial and accounting, human resource and other specified services. For the period July 1, 2015 to December 31, 2015, the amounts NiSource billed CPG for these services were not significant. There were no material assets and liabilities of discontinued operations on the Consolidated Balance Sheets at December 31, 2015. The assets and liabilities of discontinued operations on the Consolidated Balance Sheets at December 31, 2014 were: December 31, 2014 (in millions) Columbia Pipeline Group Operations Current Assets Cash and cash equivalents $ 0.5 Accounts receivable, net 149.3 Gas inventory 4.8 Materials and supplies, at average cost 24.9 Exchange gas receivable 34.8 Regulatory assets 6.1 Prepayments and other 63.0 Total current assets $ 283.4 Noncurrent Assets Net property, plant and equipment $ 4,959.7 Goodwill 1,975.5 Unconsolidated affiliates 444.3 Other investments 5.6 Regulatory assets 151.9 Deferred charges and other 9.0 Total noncurrent assets $ 7,546.0 December 31, 2014 (in millions) Columbia Pipeline Group Operations Current Liabilities Accounts payable $ 60.5 Customer deposits and credits 13.4 Taxes accrued 106.9 Exchange gas payable 34.7 Deferred revenue 22.2 Regulatory liabilities 1.3 Accrued liability for postretirement and postemployment benefits 0.6 Legal and environmental 1.5 Accrued capital expenditures 61.1 Other accruals 66.8 Total current liabilities $ 369.0 Noncurrent Liabilities Deferred income taxes $ 1,214.3 Deferred investment tax credits 0.2 Deferred credits 0.2 Accrued liability for postretirement and postemployment benefits (1) (58.0 ) Regulatory liabilities 294.2 Asset retirement obligations 23.2 Other noncurrent liabilities 84.3 Total noncurrent liabilities $ 1,558.4 (1) Represents Columbia Pipeline Group segment's overfunded position in NiSource's net underfunded other postretirement plan.

Property, Plant And Equipment

Property, Plant And Equipment	12 Months Ended
	Dec. 31, 2015
Property, Plant and Equipment [Abstract]
Property, Plant And Equipment	Property, Plant and Equipment NiSource’s property, plant and equipment on the Consolidated Balance Sheets are classified as follows: At December 31, (in millions) 2015 2014 Property Plant and Equipment Gas Distribution Utility (1) $ 10,620.4 $ 9,753.9 Electric Utility (1) 7,765.7 7,160.0 Common Utility 107.2 181.5 Construction Work in Process 453.6 573.0 Non-Utility and Other 41.2 43.1 Total Property, Plant and Equipment $ 18,988.1 $ 17,711.5 Accumulated Depreciation and Amortization Gas Distribution Utility (1) $ (3,029.0 ) $ (2,922.7 ) Electric Utility (1) (3,767.7 ) (3,596.5 ) Common Utility (56.7 ) (110.3 ) Non-Utility and Other (23.2 ) (24.6 ) Total Accumulated Depreciation and Amortization $ (6,876.6 ) $ (6,654.1 ) Net Property, Plant and Equipment $ 12,111.5 $ 11,057.4 (1) NIPSCO’s common utility plant and associated accumulated depreciation and amortization are allocated between Gas Distribution Utility and Electric Utility Property, Plant and Equipment.

Goodwill And Other Intangible A

Goodwill And Other Intangible Assets	12 Months Ended
	Dec. 31, 2015
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill And Other Intangible Assets	Goodwill and Other Intangible Assets The following presents NiSource's goodwill balance allocated by segment as of December 31, 2015: (in millions) Gas Distribution Operations Electric Operations Corporate and Other Total Goodwill $ 1,690.7 $ — $ — $ 1,690.7 Goodwill previously allocated to the former Columbia Pipeline Group Operations segment was disposed of in conjunction with the Separation. For prior periods, such balances are presented within "Assets of discontinued operations" on the Consolidated Balance Sheets. There were no other changes to the goodwill balance during 2015. NiSource's intangible assets, apart from goodwill, consist of franchise rights, which were identified as part of the purchase price allocations associated with the acquisition in February 1999 of Columbia of Massachusetts. These amounts were $253.7 million and $264.7 million , net of accumulated amortization of $188.5 million and $177.5 million , at December 31, 2015 and 2014, respectively and are being amortized over forty years from the date of acquisition. NiSource recorded amortization expense of $11.0 million in 2015, 2014, and 2013 related to its intangible assets. NiSource expects amortization expense to be $11.0 million per year for 2016-2020.

Asset Retirement Obligations

Asset Retirement Obligations	12 Months Ended
	Dec. 31, 2015
Asset Retirement Obligation [Abstract]
Asset Retirement Obligations	Asset Retirement Obligations Changes in NiSource’s liability for asset retirement obligations for the years 2015 and 2014 are presented in the table below: (in millions) 2015 2014 Beginning Balance $ 136.2 $ 148.1 Accretion recorded as a regulatory asset/liability 8.6 8.2 Additions 6.5 0.3 Settlements (7.0 ) (2.2 ) Change in estimated cash flows (1) 109.7 (18.2 ) Ending Balance $ 254.0 $ 136.2 (1) The change in estimated cash flows for 2015 is primarily attributable to estimated costs associated with the EPA's final rule for regulation of CCRs and changes to cost estimates for certain solid waste management units. See Note 18, "Other Commitments and Contingencies," for additional information on CCRs. The change in estimated cash flows for 2014 is primarily attributed to changes in estimated costs and settlement timing for electric generating stations and to retire pipeline. NiSource has recognized asset retirement obligations associated with various legal obligations including costs to remove and dispose of certain construction materials located within many of NiSource’s facilities, certain costs to retire pipeline, removal costs for certain underground storage tanks, removal of certain pipelines known to contain PCB contamination, closure costs for certain sites including ash ponds, solid waste management units and a landfill, as well as some other nominal asset retirement obligations. NiSource has a significant obligation associated with the decommissioning of its two hydro facilities located in Indiana. These hydro facilities have an indeterminate life, and no asset retirement obligation has been recorded. Certain costs of removal that have been, and continue to be, included in depreciation rates and collected in the service rates of the rate-regulated subsidiaries are classified as Regulatory liabilities on the Consolidated Balance Sheets.

Regulatory Matters

Regulatory Matters	12 Months Ended
	Dec. 31, 2015
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory Matters	Regulatory Matters Regulatory Assets and Liabilities NiSource follows the accounting and reporting requirements of ASC Topic 980, which provides that regulated entities account for and report assets and liabilities consistent with the economic effect of regulatory rate-making procedures if the rates established are designed to recover the costs of providing the regulated service and it is probable that such rates can be charged and collected. Certain expenses and credits subject to utility regulation or rate determination normally reflected in income or expense are deferred on the balance sheet and are recognized in the income statement as the related amounts are included in customer rates and recovered from or refunded to customers. Regulatory assets were comprised of the following items: At December 31, (in millions) 2015 2014 Assets Unrecognized pension benefit and other postretirement benefit costs (see Note 10) $ 928.7 $ 910.3 Other postretirement costs 47.0 46.7 Environmental costs (see Note 18-C) 62.2 65.9 Regulatory effects of accounting for income taxes (see Note 1-U) 234.1 231.8 Underrecovered gas costs (see Note 1-P and 1-Q) 34.8 32.0 Depreciation (see Note 1-H) 124.5 116.4 Uncollectible accounts receivable deferred for future recovery 17.0 26.1 Post-in-service carrying charges 107.2 87.8 EERM operation and maintenance and depreciation deferral 48.1 31.1 Sugar Creek carrying charges and deferred depreciation (see Note 1-H) 28.2 42.5 DSM Program 35.6 37.9 Other 139.3 135.4 Total Assets $ 1,806.7 $ 1,763.9 Less amounts included as Underrecovered gas cost (34.8 ) (32.0 ) Total Regulatory Assets reflected in Current Regulatory Assets and Other Regulatory Assets $ 1,771.9 $ 1,731.9 Regulatory liabilities were comprised of the following items: At December 31, (in millions) 2015 2014 Liabilities Overrecovered gas and fuel costs (see Notes 1-P and 1-Q) $ 148.1 $ 45.6 Cost of removal (see Note 6) 1,261.5 1,287.0 Regulatory effects of accounting for income taxes (see Note 1-U) 34.2 42.3 Unrecognized pension benefit and other postretirement benefit costs (see Note 10) 8.1 10.1 Other postretirement costs 38.8 31.9 Other 91.1 69.4 Total Liabilities $ 1,581.8 $ 1,486.3 Less amounts included as Overrecovered gas and fuel cost (148.1 ) (45.6 ) Total Regulatory Liabilities reflected in Current Regulatory Liabilities and Other Regulatory Liabilities and Other Removal Costs $ 1,433.7 $ 1,440.7 Regulatory assets, including underrecovered gas and fuel cost, of approximately $1,668.7 million as of December 31, 2015 are not earning a return on investment. Regulatory assets of approximately $1,544.0 million include expenses that are recovered as components of the cost of service and are covered by regulatory orders. These costs are recovered over a remaining life of up to 41 years. Regulatory assets of approximately $262.7 million at December 31, 2015 , require specific rate action. As noted below, regulatory assets for which costs have been incurred or accrued are included (or expected to be included, for costs incurred subsequent to the most recently approved rate case) in certain companies’ rate base, thereby providing a return on invested costs. Certain regulatory assets do not result from cash expenditures and therefore do not represent investments included in rate base or have offsetting liabilities that reduce rate base. Assets: Unrecognized pension benefit and other postretirement benefit costs – In 2007, NiSource adopted certain updates of ASC 715 which required, among other things, the recognition in other comprehensive income or loss of the actuarial gains or losses and the prior service costs or credits that arise during the period but that are not immediately recognized as components of net periodic benefit costs. Certain subsidiaries defer the costs as a regulatory asset in accordance with regulatory orders or as a result of regulatory precedent, to be recovered through base rates. Other postretirement costs – Primarily comprised of costs approved through rate orders to be collected through future base rates, revenue riders or tracking mechanisms. Environmental costs – Includes certain recoverable costs of investigating, testing, remediating and other costs related to gas plant sites, disposal sites or other sites onto which material may have migrated. Certain companies defer the costs as a regulatory asset in accordance with regulatory orders, to be recovered in future base rates, billing riders or tracking mechanisms. Regulatory effects of accounting for income taxes – Represents the deferral and under collection of deferred taxes in the rate making process. In prior years, NiSource has lowered customer rates in certain jurisdictions for the benefits of accelerated tax deductions. Amounts are expensed for financial reporting purposes as NiSource recovers deferred taxes in the rate making process. Underrecovered gas and fuel costs – Represents the difference between the costs of gas and fuel and the recovery of such costs in revenue, and is used to adjust future billings for such deferrals on a basis consistent with applicable state-approved tariff provisions. Recovery of these costs is achieved through tracking mechanisms. Depreciation – Primarily relates to the difference between the depreciation expense recorded by Columbia of Ohio due to a regulatory order and the depreciation expense recorded in accordance with GAAP. The regulatory asset is currently being amortized over the life of the assets. Also included is depreciation associated with the Columbia of Ohio IRP and capital expenditure program. Recovery of these costs is achieved through base rates and rider mechanisms. Refer to Note 1-H for more information. Uncollectible accounts receivable deferred for future recovery – Represents the difference between certain uncollectible expenses and the recovery of such costs to be collected through cost tracking mechanisms per regulatory orders. Post-in-service carrying charges – Columbia of Ohio has approval from the PUCO by regulatory order to defer debt-based post-in-service carrying charges as a regulatory asset for future recovery. As such, Columbia of Ohio defers a debt-based carrying charge on eligible property, plant and equipment from the time it is placed into utility service until recovery of the property, plant and equipment is included in customer rates in base rates or through a rider mechanism. Inclusion in customer rates generally occurs when Columbia of Ohio files its next rate proceeding following the in-service date of the property, plant and equipment. EERM operation and maintenance and depreciation deferral – NIPSCO obtained approval from the IURC to recover certain environmental related costs including operation and maintenance and depreciation expense once the environmental facilities become operational. Recovery of these costs will continue until such assets are included in rate base through an electric base rate case. The EERM deferred charges represent expenses that will be recovered from customers through an annual EERM Cost Tracker which authorizes the collection of deferred balances over a twelve month period. Sugar Creek carrying charges and deferred depreciation – The IURC approved the deferral of debt-based carrying charges and the deferral of depreciation expense for the Sugar Creek assets. NIPSCO continued to defer such amounts until new electric rates were approved and implemented on December 27, 2011. Balances are being amortized over five years beginning January 2012. As of December 31, 2015 , the remaining unamortized balance is $14.3 million . An additional $13.9 million is deferred for consideration in NIPSCO's current electric base rate case. Management believes this amount is probable of recovery through future rates. DSM Program - Represents costs associated with Gas Distribution Operations and Electric Operations companies' energy efficiency and conservation programs. Costs are recovered through tracking mechanisms. Liabilities: Overrecovered gas and fuel costs – Represents the difference between the cost of gas and fuel and the recovery of such costs in revenues, and is the basis to adjust future billings for such recoveries on a basis consistent with applicable state-approved tariff provisions. Refunding of these revenues is achieved through tracking mechanisms. Cost of removal – Represents anticipated costs of removal that have been, and continue to be, included in depreciation rates and collected in customer rates of the rate-regulated subsidiaries for future costs to be incurred. Regulatory effects of accounting for income taxes – Represents amounts owed to customers for deferred taxes collected at a higher rate than the current statutory rates and liabilities associated with accelerated tax deductions owed to customers that are established during the rate making process. Unrecognized pension benefit and other postretirement benefit costs – In 2007, NiSource adopted certain updates of ASC 715 which required, among other things, the recognition in other comprehensive income or loss of the actuarial gains or losses and the prior service costs or credits that arise during the period but that are not immediately recognized as components of net periodic benefit costs. Certain subsidiaries defer the costs as a regulatory liability in accordance with regulatory orders or as a result of regulatory precedent, to be refunded through base rates. Other postretirement costs – Primarily represents cash contributions in excess of postretirement benefit expense that is deferred as a regulatory liability by certain subsidiaries in accordance with regulatory orders. Gas Distribution Operations Regulatory Matters Significant Rate Developments . On April 30, 2013, Indiana Governor Pence signed Senate Enrolled Act 560, the TDSIC statute, into law. Among other provisions, this legislation provides for cost recovery outside of a base rate proceeding for new or replacement electric and gas transmission, distribution, and storage projects that a public utility undertakes for the purposes of safety, reliability, system modernization, or economic development. Provisions of the TDSIC statute require that, among other things, requests for recovery include a seven-year plan of eligible investments. Once the plan is approved by the IURC, 80 percent of eligible costs can be recovered using a periodic rate adjustment mechanism. The cost recovery mechanism is referred to as a TDSIC mechanism. Recoverable costs include a return on, and of, the investment, including AFUDC, post-in-service carrying charges, operation and maintenance expenses, depreciation, and property taxes. The remaining 20 percent of recoverable costs are to be deferred for future recovery in the public utility’s next general rate case. The periodic rate adjustment mechanism is capped at an annual increase of no more than two percent of total retail revenues. On April 30, 2014, the IURC issued an order approving NIPSCO's gas TDSIC seven-year plan. On May 29, 2014, the NIPSCO Industrial Group filed a Notice of Appeal with the Indiana Court of Appeals in response to the IURC's April 30, 2014 ruling. Subsequently, the NIPSCO Industrial Group filed a Voluntary Notice of Dismissal, which was granted with prejudice. On January 28, 2015, the IURC issued an order approving NIPSCO's gas TDSIC-1 and a revised gas TDSIC seven-year plan of eligible investments for a total of approximately $840 million with the IURC. On August 31, 2015, NIPSCO filed TDSIC-3 which included an updated seven-year plan of approximately $817 million with the IURC. An order is expected in the first quarter of 2016. On November 28, 2012, the PUCO approved Columbia of Ohio’s application to extend its Infrastructure Replacement Program for an additional five years, allowing Columbia of Ohio to continue to invest and recover on its accelerated main replacements. On November 25, 2014, Columbia of Ohio filed a Notice of Intent to file an application to adjust rates associated with its IRP and DSM Riders. Columbia of Ohio filed its Application on February 27, 2015, and requested authority to increase revenues by $24.7 million . On March 26, 2015, PUCO Staff filed Comments recommending that the PUCO approve Columbia of Ohio’s application in full. On April 22, 2015, the PUCO issued an Order that approved Columbia of Ohio's application. New rates went into effect on May 1, 2015. Now in the third year of the extended program, Columbia of Ohio filed a Notice of Intent on November 25, 2015 to file an application to adjust rates associated with its IRP and DSM Riders. The Notice of Intent states that Columbia of Ohio will file an Application by February 28, 2016, in which it will request authority to increase revenues by up to $33.2 million . On September 12, 2014, Columbia of Ohio filed an application that seeks authority to establish a regulatory asset and defer, for accounting and financial reporting purposes, the expenditures to be incurred in implementing Columbia of Ohio’s Pipeline Safety Program. Columbia of Ohio requested authority to defer Pipeline Safety Program costs of up to $15.0 million annually. By Order dated December 17, 2014, the PUCO approved Columbia of Ohio’s application, approving a deferral of up to $15.0 million annually. As of December 31, 2015, Columbia of Ohio has deferred $11.6 million related to the program. On December 24, 2012, Columbia of Ohio filed an application for authority to continue its capital expenditure program in 2013 and succeeding years, and for the authority to defer the related post-in-service carrying charges, depreciation expense, and property taxes on the assets of the capital expenditure program placed into service. As of December 31, 2015, Columbia of Ohio has deferred $57.6 million related to the program. On March 19, 2015, Columbia of Pennsylvania filed a base rate case with the Pennsylvania PUC, seeking a revenue increase of $46.2 million annually. The case was driven by Columbia of Pennsylvania’s ongoing capital investment program which exceeded $197.0 million in 2015 and is projected to exceed $220.0 million in 2016, as well as operation and maintenance expenditures related to employee training and compliance with pipeline safety regulations. Columbia of Pennsylvania's request for rate relief included the recovery of costs that will be incurred after the implementation of new rates, as authorized by the Pennsylvania General Assembly with the passage of Act 11 of 2012. On August 27, 2015, the parties to the case filed a joint petition for approval of a settlement that features an annual revenue increase of $28.0 million . The Pennsylvania PUC approved the petition on December 3, 2015, and Columbia of Pennsylvania implemented new rates on December 18, 2015. On April 30, 2014, Columbia of Virginia filed a base rate case with the VSCC seeking an annual revenue increase of $31.8 million . New rates went into effect in October 2014, subject to refund. On December 10, 2014, Columbia of Virginia presented at hearing a Stipulation and Proposed Recommendation (“Stipulation”) executed by certain parties to the rate proceeding that included a base revenue increase of $25.2 million including recovery of costs related to the implementation of pipeline safety programs. On March 30, 2015, the VSCC issued an Order Remanding for Further Action approving the revenue increase of $25.2 million contained in the Stipulation, but remanding for further proceedings the single issue of the manner in which fixed costs were to be assigned to the fixed customer charges of each rate class. Following a hearing, the VSCC on August 21, 2015 issued a Final Order resolving the fixed customer charge and allowing Columbia of Virginia to implement new rates. On July 7, 2014, the Governor of Massachusetts signed into law Chapter 149 of the Acts of 2014, An Act Relative to Natural Gas Leaks (“the Act’). The Act authorizes natural gas distribution companies to file gas infrastructure replacement plans with the Massachusetts DPU to address the replacement of aging natural gas pipeline infrastructure. In addition, the Act provides that the Massachusetts DPU may, after review of the plans, allow the proposed estimated costs of the plan into rates as of May 1 of the subsequent year. Pursuant to the Act, Columbia of Massachusetts filed its first Gas System Enhancement Program (“GSEP”) plan on October 31, 2014, for the 2015 construction year (“2015 GSEP”) proposing to recover $2.6 million . After review, the Massachusetts DPU approved the Columbia of Massachusetts’s 2015 GSEP for effect May 1, 2015 and, in accordance with the Act, Columbia of Massachusetts will file the reconciliation of the 2015 GSEP on May 1, 2016. On October 30, 2015, Columbia of Massachusetts filed its GSEP for the 2016 construction year. Columbia of Massachusetts proposed to recover an increment of $6.4 million for the costs associated with the replacement of eligible leak-prone infrastructure during the 2016 construction year for a cumulative proposed revenue requirement recovery of $9.0 million effective May 1, 2016. The Massachusetts DPU is currently reviewing the plan and is expected to issue an order prior to May 1, 2016. On October 30, 2009, the Massachusetts DPU approved Columbia of Massachusetts's revenue decoupling mechanism that was filed in its base rate case. This allows Columbia of Massachusetts to apply annual adjustments to its Peak and Off-peak rates. On March 16, 2015, Columbia of Massachusetts filed its Off-peak Period RDAF in the amount of $2.5 million for effect May 1, 2015. The Massachusetts DPU approved the rate for effect May 1, 2015, pending further review and investigation. On August 5, 2015, the Massachusetts DPU issued its final order approving the rate. On September 17, 2015, Columbia of Massachusetts filed its Peak Period RDAF in the amount of a credit to customers of $17.1 million for effect November 1, 2015. The Massachusetts DPU approved the rate for effect November 1, 2015, pending further review and investigation. On April 16, 2015, Columbia of Massachusetts filed a base rate case with the Massachusetts DPU. The case, which sought increased annual revenues of approximately $49.0 million , was designed to support Columbia of Massachusetts's continued focus on providing safe and reliable service in compliance with increasing state and federal regulations and oversight, and recovery of associated increased operations and maintenance costs. Columbia of Massachusetts arrived at a settlement agreement with the Massachusetts Attorney General in the case which was filed for approval with the Massachusetts DPU on August 19, 2015 and approved on October 7, 2015. The settlement agreement provides for increased annual revenues of $32.8 million beginning November 1, 2015, with an additional $3.6 million annual increase in revenues starting November 1, 2016. The settlement also provides that Columbia of Massachusetts cannot increase base distribution rates to become effective prior to November 1, 2018. Columbia of Massachusetts's LDAF allows for the recovery of costs related to pension and other postretirement expense, low income programs, environmental remediation programs, Attorney General expert witness costs and energy efficiency programs. This allows Columbia of Massachusetts to file semi-annually to recover the cost in Peak and Off-peak rates. On January 20, 2015, Columbia of Massachusetts filed its 2015 Off-Peak Period LDAF with a proposed effective date of May 1, 2015. The 2015 Off-Peak Period LDAF of $70 million was approved on April 30, 2015, for effect May 1, 2015. On July 30, 2015, Columbia of Massachusetts filed its 2015-2016 Peak Period LDAF and on September 17, 2015, Columbia of Massachusetts filed its 2015 PEF and 2015 RAAF, each with a proposed effective date of November 1, 2015. The 2015-2016 Peak Period LDAF of $49.7 million effective November 1, 2015 was approved on October 30, 2015. The 2015 PEF and 2015 RAAF components of the LDAF were approved subject to further investigation and reconciliation. On August 7, 2015, Columbia of Maryland filed a base rate proceeding with the Maryland PSC, seeking an annual revenue increase of approximately $0.7 million . The matter was fully litigated. On November 4, 2015, the Maryland PSC issued an Order granting Columbia of Maryland authority to adjust its rates to produce an annual revenue increase of $0.5 million . The new rates went into effect on November 5, 2015. Cost Recovery and Trackers . A significant portion of the distribution companies' revenue is related to the recovery of gas costs, the review and recovery of which occurs via standard regulatory proceedings. All states require periodic review of actual gas procurement activity to determine prudence and to permit the recovery of prudently incurred costs related to the supply of gas for customers. NiSource distribution companies have historically been found prudent in the procurement of gas supplies to serve customers. Certain operating costs of the NiSource distribution companies are significant, recurring in nature, and generally outside the control of the distribution companies. Some states allow the recovery of such costs via cost tracking mechanisms. Such tracking mechanisms allow for abbreviated regulatory proceedings in order for the distribution companies to implement charges and recover appropriate costs. Tracking mechanisms allow for more timely recovery of such costs as compared with more traditional cost recovery mechanisms. Examples of such mechanisms include GCR adjustment mechanisms, tax riders, and bad debt recovery mechanisms. Comparability of Gas Distribution Operations line item operating results is impacted by regulatory trackers that allow for the recovery in rates of certain costs such as bad debt expenses. Increases in the expenses that are the subject of trackers, result in a corresponding increase in net revenues and therefore have essentially no impact on total operating income results. Certain of the NiSource distribution companies have completed rate proceedings involving infrastructure replacement or are embarking upon regulatory initiatives to replace significant portions of their operating systems that are nearing the end of their useful lives. Each LDC's approach to cost recovery may be unique, given the different laws, regulations and precedent that exist in each jurisdiction. As further discussed above, NIPSCO has approval from the IURC to recover certain costs for transmission, distribution and storage system improvements. On January 28, 2015, the IURC issued an order approving NIPSCO’s gas TDSIC-1. The Order approved $4.4 million of net capital expenditures for the period ended June 30, 2014 and granted ratemaking relief and accounting treatment. On February 27, 2015, NIPSCO filed gas TDSIC-2 which included $43.3 million of net capital expenditures for the period ended December 31, 2014. Given the Indiana Court of Appeals decision in NIPSCO's electric TDSIC filing (for further information, see "Electric Operations Regulatory Matters" below), NIPSCO elected to dismiss its TDSIC-2 filing in favor of supplying further detailed plan updates in the next proceeding, TDSIC-3. On August 31, 2015, NIPSCO filed TDSIC-3 which included $75.2 million of net capital expenditures for the period ended June 30, 2015. An order is expected in the first quarter of 2016. Electric Operations Regulatory Matters Significant Rate Developments . As part of a multi-state effort to strengthen the electric transmission system serving the Midwest, NIPSCO is currently investing in two projects that were authorized by the MISO and are scheduled to be in service during the latter part of the decade. On July 19, 2012 and December 19, 2012, the FERC issued orders approving construction work in progress in rate base and abandoned plant cost recovery requested by NIPSCO for the 100-mile, 345 kV transmission project and its right to develop 50 percent of the 66-mile, 765 kV project. On December 19, 2012, the FERC issued an order authorizing NIPSCO's request to transition to forward looking rates, allowing more timely recovery of NIPSCO's investment in transmission assets. On August 22, 2012, the IURC issued an order authorizing NIPSCO to retain certain revenues under MISO Schedule 26-A. NIPSCO began recording revenue in the first quarter of 2013 using a forward looking rate. These projects involve an investment of approximately $450 million for NIPSCO and are anticipated to be in service by the end of 2018. On November 12, 2013, several complainants filed in opposition at the FERC regarding the 12.38% base ROE used to set the MISO Transmission Owners' transmission rates and requested a reduction in the base ROE to 9.15% . The complaint requested that the FERC limit the capital structure of MISO Transmission Owners to no more than 50% common equity for ratemaking purposes and that the FERC eliminate incentive adders for membership in a RTO. On October 16, 2014, the FERC issued an Order that dismissed the portions of the complaint that challenged Transmission Owner capital structures and incentive adders; set the base ROE for hearing and suspended it to allow for settlement; set a refund effective date of November 12, 2013; and directed the parties to the new two-step discounted cash flow methodology established by the FERC. On December 22, 2015, the Administrative Law Judge issued an Initial Decision which authorized the MISO Transmission Owners to collect a base ROE of 10.32% for the period of November 12, 2013 through February 11, 2015. The Initial Decision is subject to approval by the full Commission and is not a final order. On January 5, 2015, the FERC approved a 50-basis point adder for the MISO Transmission Owners based on their continued participation in MISO. The FERC established an effective date for the adder of January 6, 2015 but suspended collection of the adder for billing purposes until the November 12, 2013 complaint is resolved. On February 12, 2015, a second group of complainants filed in opposition to the 12.38% base ROE, requesting a refund effective date of February 12, 2015 and recommended a base ROE of 8.67% . Hearings commenced on February 16, 2016 and the FERC anticipates that an initial decision will be issued on the second complaint by June 30, 2016. NIPSCO recorded a liability of $3.4 million related to the complaints and will continue to adjust the liability for ongoing activity. On July 19, 2013, NIPSCO filed its electric TDSIC with the IURC. The filing included the seven-year plan of eligible investments for a total of approximately $1.1 billion with the majority of the spend occurring in years 2016 through 2020. On February 17, 2014, the IURC issued an order approving NIPSCO’s seven-year plan of eligible investments. The order also granted NIPSCO ratemaking relief associated with the eligible investments through a rate adjustment mechanism. The NIPSCO Industrial Group and the OUCC filed Notices of Appeal with the Indiana Court of Appeals in response to the IURC's ruling. On November 25, 2014, NIPSCO’s requested TDSIC factors were approved on an interim basis and subject to refund, pending the outcome of the appeals of the IURC’s February 17, 2014 Orders. On April 8, 2015, the Court of Appeals issued an order concluding that the IURC erred in approving NIPSCO’s seven-year plan given its lack of detail regarding the projects for years two through seven. The court then remanded the decision to the IURC. On May 26, 2015, NIPSCO filed a settlement on remand which, among other things, requires NIPSCO to file an electric base rate case proceeding by December 31, 2015 and a new seven-year electric TDSIC plan following the filing of its next general rate case proceeding. The settlement agreement was rejected by the IURC on September 23, 2015. The settling parties filed a Petition for Rehearing on September 29, 2015 and were granted a rehearing which was held on October 28, 2015. On December 16, 2015, the IURC issued an Order on Remand approving the settlement agreement and NIPSCO’s seven-year electric plan as set forth in the remand proceeding, subject to certain modifications. On December 31, 2015, NIPSCO filed a new electric seven-year plan of eligible investments for a total of approximately $1.3 billion covering spend in years 2016 through 2022. NIPSCO expects to make a TDSIC rate adjustment mechanism filing later in 2016 to seek recovery and ratemaking relief of such investments. NIPSCO expects a final order in the seven-year plan filing in the third quarter of 2016. On October 1, 2015, NIPSCO filed an electric base rate case with the IURC, seeking a revenue increase of approximately $148.0 million . As part of this filing, NIPSCO is proposing to update base rates for previously incurred infrastructure improvements, revised depreciation rates, and the inclusion of previously approved environmental and federally mandated compliance costs. A final order is anticipated in the third quarter of 2016. On November 12, 2014, the IURC issued an Order approving NIPSCO’s 2015 proposed electric energy efficiency programs along with the continued authority to defer and recover the related 2015 program costs estimated to be $18.6 million and associated lost margins. On December 30, 2015, the IURC approved, with modifications, NIPSCO’s electric energy efficiency programs and budgets through December 31, 2018, including authorization to use its energy efficiency recovery mechanism to recover program costs and lost margins, the latter capped at the lesser of four years or the life of the measure. Cost Recovery and Trackers . A significant portion of NIPSCO's revenue is related to the recovery of fuel costs to generate power and the fuel costs related to purchased power. These costs are recovered through a FAC, a quarterly, regulatory proceeding in Indiana. Certain operating costs of the Electric Operations are significant, recurring in nature, and generally outside the control of NIPSCO. The IURC allows for recovery of such costs via cost tracking mechanisms. Such tracking mechanisms allow for abbreviated regulatory proceedings in order for NIPSCO to implement charges and recover appropriate costs. Tracking mechanisms allow for more timely recovery of such costs as compared with more traditional cost recovery mechanisms. Examples of such mechanisms include electric energy efficiency programs, MISO non-fuel costs and revenues, resource capacity charges, and environmental related costs. NIPSCO has approval from the IURC to recover certain environmental related costs through an ECT. Under the ECT, NIPSCO is permitted to recover (1) AFUDC and a return on the capital investment expended by NIPSCO to implement environmental compliance plan projects through an ECRM and (2) related operation and maintenance and depreciation expenses once the environmental facilities become operational through an EERM. On October 21, 2015, the IURC issued an order on ECR-26 approving NIPSCO’s request to begin earning a return on $776.5 million of net capital expenditures for the period ended June 30, 2015. The order also approved a revised capital cost estimate of $255.3 million for its Phase III multi-pollutant compliance plan projects related to the Michigan City Unit 12 FGD, a decrease from the previous IURC approved cost estimate of $264.8 million and a revised MATS capital cost estimate of $48.6 million , a decrease from the previous IURC approved cost estimate of $59.3 million . On January 29, 2016, NIPSCO filed ECR-27 which included $800.7 million of net capital expenditures for the period ended December 31, 2015. An order is expected in the second quarter of 2016. As further discussed above, NIPSCO has approval from the IURC to recover certain costs for transmission and distribution system improvements through the electric TDSIC. On November 25, 2014, the IURC approved, on an interim basis and subject to refund pending the outcome of appeals, NIPSCO’s requested TDSIC factors associated with the eligible investments, which included $19.4 million of net capital expenditures for the period ended June 30, 2014. As a result of the December 16, 2015 IURC Order on Remand described above, NIPSCO began refunding all monies that were collected through the electric TDSIC mechanism pursuant to the November 25, 2014 IURC order. NIPSCO was authorized to defer, as a regulatory asset, 100% of all TDSIC costs incurred since March 1, 2014 in connection with its 2014 and 2015 eligible TDSIC investments, as specified in the December 16, 2015 Order on Remand, until such deferral is recovered as part of a gen

Variable Interest Entities

Variable Interest Entities	12 Months Ended
	Dec. 31, 2015
Variable Interest Entities And Equity Investments [Abstract]
Variable Interest Entities And Equity Method Investments	Variable Interest Entities In general, a VIE is an entity (1) that has an insufficient amount of at-risk equity to permit the entity to finance its activities without additional financial subordinated support provided by any other parties, (2) whose at-risk equity owners, as a group, do not have power, through voting rights or similar rights, to direct activities of the entity that most significantly impact the entity’s economic performance or (3) whose at-risk owners do not absorb the entity’s losses or receive the entity’s residual return. A VIE is required to be consolidated by a company if that company is determined to be the primary beneficiary of the VIE. NiSource would consolidate those VIEs for which it was the primary beneficiary. NiSource considers quantitative and qualitative elements in determining the primary beneficiary. Qualitative measures include the ability to control an entity and the obligation to absorb losses or the right to receive benefits from such entity. NiSource’s analysis includes an assessment of guarantees, operating leases, purchase agreements, and other contracts, as well as its investments and joint ventures. For items that have been identified as variable interests, or where there is involvement with an identified VIE, an in-depth review of the relationship between the relevant entities and NiSource is made to evaluate qualitative and quantitative factors to determine the primary beneficiary, if any, and whether additional disclosures would be required under the current standard. NIPSCO has a service agreement with Pure Air, a general partnership between Air Products and Chemicals, Inc. and First Air Partners LP, under which Pure Air provides scrubber services to reduce sulfur dioxide emissions for Units 7 and 8 at the Bailly Generating Station. Services under this contract commenced on July 1, 1992 and expired on June 30, 2012. The agreement was renewed effective July 1, 2012 for ten years and NIPSCO will continue to pay for the services under a combination of fixed and variable charges. NiSource has made an exhaustive effort to obtain information needed from Pure Air to determine the status of Pure Air as a VIE. However, NIPSCO has not been able to obtain this information and, as a result, it is unclear whether Pure Air is a VIE and if NIPSCO is the primary beneficiary. NIPSCO will continue to request the information required to determine whether Pure Air is a VIE. NIPSCO has no exposure to loss related to the service agreement with Pure Air and payments under this agreement were $ 19.5 million and $ 23.0 million for the years ended December 31, 2015 and 2014 , respectively. In accordance with GAAP, the renewed agreement was evaluated to determine whether the arrangement qualifies as a lease. Based on the terms of the agreement, the arrangement qualified for capital lease accounting. As the effective date of the new agreement was July 1, 2012, NiSource capitalized this lease beginning in the third quarter of 2012.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The components of income tax expense were as follows: Year Ended December 31, (in millions) 2015 2014 2013 Income Taxes Current Federal $ — $ — $ (11.6 ) State 6.0 5.4 1.8 Total Current 6.0 5.4 (9.8 ) Deferred Federal 124.1 129.5 125.6 State 13.6 35.4 (3.4 ) Total Deferred 137.7 164.9 122.2 Deferred Investment Credits (2.4 ) (3.5 ) (3.8 ) Income Taxes from Continuing Operations $ 141.3 $ 166.8 $ 108.6 Total income taxes from continuing operations were different from the amount that would be computed by applying the statutory federal income tax rate to book income before income tax. The major reasons for this difference were as follows: Year Ended December 31, (in millions) 2015 2014 2013 Book income from Continuing Operations before income taxes $ 339.9 $ 423.0 $ 329.6 Tax expense at statutory federal income tax rate 118.9 35.0 % 148.1 35.0 % 115.4 35.0 % Increases (reductions) in taxes resulting from: State income taxes, net of federal income tax benefit 14.8 4.4 15.7 3.7 2.3 0.7 Regulatory treatment of depreciation differences 4.3 1.3 0.7 0.2 (0.5 ) (0.2 ) Amortization of deferred investment tax credits (2.4 ) (0.7 ) (3.5 ) (0.8 ) (3.8 ) (1.2 ) Nondeductible expenses 2.1 0.6 0.8 0.2 2.4 0.7 Employee stock ownership plan dividends (2.9 ) (0.9 ) (3.8 ) (0.9 ) (3.6 ) (1.0 ) AFUDC equity (3.5 ) (1.0 ) (3.5 ) (0.8 ) (3.4 ) (1.0 ) Charitable contribution carryover 17.8 5.2 — — — — Tax accrual adjustments and other, net (7.8 ) (2.3 ) 12.3 2.8 (0.2 ) (0.1 ) Income Taxes from Continuing Operations $ 141.3 41.6 % $ 166.8 39.4 % $ 108.6 32.9 % The effective income tax rates were 41.6% , 39.4% and 32.9% in 2015 , 2014 and 2013 , respectively. The 2.2% increase in the overall effective tax rate in 2015 versus 2014 was primarily the result of a $17.8 million increase in federal income tax expense associated with write downs of charitable contribution carryovers discussed below, offset by a $10.5 million decrease in income tax expense related to state apportionment changes and permanent items as a result of remeasurement after the Separation. The 6.5% increase in the overall effective tax rate in 2014 versus 2013 was primarily a result of a $13.5 million increase in tax expense related to state apportionment changes and permanent items, a $7.1 million increase due to Indiana state taxes discussed below, a $5.4 million increase in tax expense due to Pennsylvania regulatory changes discussed below, and $4.1 million of additional state income tax expense related to corporate restructuring. On December 18, 2015, the President signed into law the Protecting Americans from Tax Hikes Act of 2015 (PATH). PATH, among other things, extends the research credit under U.S. Internal Revenue Code section 41 permanently and also extended and modified bonus depreciation through 2019. In general, 50% bonus depreciation is available for property placed in service before January 1, 2018, 40% bonus depreciation is available for property placed in service before January 1, 2019 and 30% bonus depreciation is available for property placed in service before January 1, 2020. NiSource recorded the effects of PATH in the fourth quarter of 2015. As a result of PATH and 50% bonus depreciation being extended, NiSource recorded tax expense of $5.8 million in 2015 for the expiration of unused charitable contribution carryforwards which expired due to the 5 year carryover limitation. NiSource also recorded a valuation allowance for an additional $12.0 million of charitable contribution carryforwards that are set to expire in 2016-2019 in the event that NiSource does not have sufficient taxable income to utilize the carryforward amounts. On March 25, 2014, the governor of Indiana signed into law Senate Bill 1, which among other things, lowers the corporate income tax rate from 6.5% to 4.9% over six years beginning on July 1, 2015. The reduction in the tax rate will impact deferred income taxes and tax-related regulatory assets and liabilities recoverable in the ratemaking process. In addition, deferred tax assets and liabilities, primarily deferred tax assets related to the Indiana net operating loss carry forward, will be reduced to reflect the lower rate at which these temporary differences and tax benefits will be realized. In the first quarter of 2014, NiSource recorded tax expense of $7.1 million to reflect the effect of this rate change. This expense is largely attributable to the remeasurement of the Indiana net operating loss at the 4.9% rate. The majority of NiSource’s tax temporary differences are related to NIPSCO’s utility plant. As a result of a Pennsylvania PUC Order dated December 3, 2015, Columbia of Pennsylvania adjusted the flow through in rates of tax benefits so that the unamortized balance of a change in accounting method for certain capitalized costs of approximately $2.0 million at December 31, 2014 would be amortized through December 2016. The amortization of excess tax benefits was $9.5 million in 2013, $4.1 million in 2014 and $1.4 million in 2015. On a prospective basis, Columbia of Pennsylvania will recognize deferred tax expense, rather than flow through in rates, the tax benefits resulting from the method change. On May 22, 2015, NiSource received an acceptance letter from the IRS for its 2011-2013 audit examination. NiSource had recorded a receivable at the end of 2014 in the amount of $6.0 million related to those tax years and in the second quarter of 2015, NiSource recognized additional net operating loss carryforwards from the IRS related to the audit examination. The recognition of the receivables and net operating loss carryforwards did not materially affect tax expense or net income. Deferred income taxes result from temporary differences between the financial statement carrying amounts and the tax basis of existing assets and liabilities. The principal components of NiSource’s net deferred tax liability were as follows: At December 31, (in millions) 2015 2014 Deferred tax liabilities Accelerated depreciation and other property differences $ 3,510.8 $ 2,964.6 Unrecovered gas and fuel costs 11.2 11.4 Other regulatory assets 403.3 610.6 Premiums and discounts associated with long-term debt 9.9 12.5 Total Deferred Tax Liabilities 3,935.2 3,599.1 Deferred tax assets Other regulatory liabilities (74.4 ) (79.3 ) Cost of removal (519.4 ) (527.7 ) Pension and other postretirement/postemployment benefits (243.8 ) (191.9 ) Environmental liabilities (45.9 ) (52.1 ) Net operating loss carryforward and Alternative Minimum Tax credit carryforward (437.4 ) (372.7 ) Other accrued liabilities (89.0 ) (58.9 ) Other, net (160.0 ) (150.7 ) Total Deferred Tax Assets (1,569.9 ) (1,433.3 ) Net Deferred Tax Liabilities $ 2,365.3 $ 2,165.8 NiSource adopted ASU 2015-17 as of December 31, 2015 and applied the provisions of the standard retrospectively. As a result, NiSource's balance sheet as of December 31, 2014 was adjusted to reclassify $272.1 million of deferred income taxes from current assets to noncurrent liabilities. Refer to Note 2, "Recent Accounting Pronouncements," for further information. State income tax net operating loss benefits are recorded at their realizable value. NiSource anticipates it is more likely than not that it will realize $34.7 million and $31.7 million of these tax benefits as of December 31, 2015 and 2014 , respectively, prior to their expiration. These tax benefits are primarily related to Indiana and Pennsylvania. The carryforward periods for these tax benefits expire in various tax years from 2025 to 2035 . The remaining net operating loss carryforward tax benefit represents a Federal carryforward of $395.4 million that will expire in 2030 and an Alternative Minimum Tax credit of $7.3 million that will carry forward indefinitely. In addition, for tax purposes, the $395.4 million discussed above is increased by $29.0 million for the effect of excess equity compensation deductions that will be realized upon the full utilization of the loss carryforward. A reconciliation of the beginning and ending amounts of unrecognized tax benefits is as follows: Reconciliation of Unrecognized Tax Benefits (in millions) 2015 2014 2013 Unrecognized Tax Benefits - Opening Balance $ 24.4 $ 23.7 $ 28.4 Gross increases - tax positions in prior period 0.4 — 1.6 Gross decreases - tax positions in prior period (23.9 ) (1.0 ) (21.4 ) Gross increases - current period tax positions — 1.7 15.1 Unrecognized Tax Benefits - Ending Balance $ 0.9 $ 24.4 $ 23.7 Offset for net operating loss carryforwards (0.9 ) (24.2 ) (23.0 ) Balance - Net of Net Operating Loss Carryforwards $ — $ 0.2 $ 0.7 The IRS issued Revenue Procedure 2013-24 on April 30, 2013, which provided guidance for repairs related to generation property. Among other things, the Revenue Procedure listed units of property and material components of units of property for purposes of analyzing repair versus capitalization issues. NiSource adopted this Revenue Procedure for income tax filings for 2014. NiSource evaluated and recorded the effect of this change in method enabled by this Revenue Procedure as of December 31, 2013. As a result of the findings received in 2015 for the 2011-2014 audit, NiSource reversed its previously recorded unrecognized tax benefits related to the requested change in tax accounting method. The reversal of the unrecognized tax benefits did not materially affect tax expense or net income. Offsetting the liability for unrecognized tax benefits are $0.9 million of related outstanding tax receivables and net operating loss carryforwards resulting in a net balance of zero , including interest, related to the tax method change issues. Except as discussed above, there have been no other material changes in 2015 to NiSource's uncertain tax positions recorded as of December 31, 2014 . The total amount of unrecognized tax benefits at December 31, 2015 , 2014 and 2013 that, if recognized, would affect the effective tax rate is $0.9 million , $4.1 million and $4.0 million , respectively. As of December 31, 2015, it is reasonably possible that a $0.9 million decrease in unrecorded tax benefits could occur in 2016 due primarily to the conclusion of the federal audit for tax year 2014. NiSource recognizes accrued interest on unrecognized tax benefits, accrued interest on other income tax liabilities and tax penalties in income tax expense. Interest expense recorded on unrecognized tax benefits and other income tax liabilities was immaterial for all periods presented. There were no accruals for penalties recorded in the Statements of Consolidated Income for the years ended December 31, 2015, 2014 and 2013 and there were no balances for accrued penalties recorded on the Consolidated Balance Sheets as of December 31, 2015 and December 31, 2014. NiSource is subject to income taxation in the United States and various state jurisdictions, primarily Indiana, West Virginia, Pennsylvania, Kentucky, Massachusetts, Maryland and New York. Because NiSource is part of the IRS’s Large and Mid-Size Business program, each year’s federal income tax return is typically audited by the IRS. As of December 31, 2015, tax years through 2013 have been audited and are effectively closed to further assessment. The audit of tax year 2014 under the CAP is expected to be completed in 2016. NiSource is also under the CAP for the audit of tax year 2015 and has been accepted into the program for the audit of tax year 2016. The statute of limitations in each of the state jurisdictions in which NiSource operates remain open until the years are settled for federal income tax purposes, at which time amended state income tax returns reflecting all federal income tax adjustments are filed. As of December 31, 2015 , there were no state income tax audits in progress that would have a material impact on the consolidated financial statements.

Pension And Other Postretiremen

Pension And Other Postretirement Benefits	12 Months Ended
	Dec. 31, 2015
Pension and Other Postretirement Benefit Expense [Abstract]
Pension and Other Postretirement Benefits Disclosure	Pension and Other Postretirement Benefits NiSource provides defined contribution plans and noncontributory defined benefit retirement plans that cover certain of its employees. Benefits under the defined benefit retirement plans reflect the employees’ compensation, years of service and age at retirement. Additionally, NiSource provides health care and life insurance benefits for certain retired employees. The majority of employees may become eligible for these benefits if they reach retirement age while working for NiSource. The expected cost of such benefits is accrued during the employees’ years of service. Current rates of rate-regulated companies include postretirement benefit costs, including amortization of the regulatory assets that arose prior to inclusion of these costs in rates. For most plans, cash contributions are remitted to grantor trusts. In connection with the Separation, NiSource entered into an Employees Matters Agreement with CPG, which provides that employees of CPG no longer participate in benefit plans sponsored by NiSource as of the Separation date. Upon the completion of the Separation, the NiSource pension and other postretirement benefit plans transferred assets and obligations to the CPG plans resulting in a net decrease in the pension plans underfunded status of $48.0 million and a net increase in the other postretirement benefit plans underfunded status of $115.9 million . The 2014 amounts included in the discussion below include balances related to CPG. Refer to Note 3, "Discontinued Operations," for additional information. NiSource Pension and Other Postretirement Benefit Plans’ Asset Management . NiSource employs a total return investment approach whereby a mix of equities and fixed income investments are used to maximize the long-term return of plan assets for a prudent level of risk. Risk tolerance is established through careful consideration of plan liabilities, plan funded status, and asset class volatility. The investment portfolio contains a diversified blend of equity and fixed income investments. Furthermore, equity investments are diversified across U.S. and non-U.S. stocks, as well as growth, value, small and large capitalizations. Other assets such as private equity funds are used judiciously to enhance long-term returns while improving portfolio diversification. Derivatives may be used to gain market exposure in an efficient and timely manner; however, derivatives may not be used to leverage the portfolio beyond the market value of the underlying assets. Investment risk is measured and monitored on an ongoing basis through quarterly investment portfolio reviews, annual liability measurements, and periodic asset/liability studies. NiSource utilizes a building block approach with proper consideration of diversification and rebalancing in determining the long-term rate of return for plan assets. Historical markets are studied and long-term historical relationships between equities and fixed income are analyzed to ensure that they are consistent with the widely accepted capital market principle that assets with higher volatility generate greater return over the long run. Current market factors such as inflation and interest rates are evaluated before long-term capital market assumptions are determined. Peer data and historical returns are reviewed to check for reasonability and appropriateness. The most important component of an investment strategy is the portfolio asset mix, or the allocation between the various classes of securities available to the pension and other postretirement benefit plans for investment purposes. The asset mix and acceptable minimum and maximum ranges established for the NiSource plan assets represents a long-term view and are listed in the table below. In 2012, a dynamic asset allocation policy for the pension fund was approved. This policy calls for a gradual reduction in the allocation to return-seeking assets (equities, real estate, private equity and hedge funds) and a corresponding increase in the allocation to liability-hedging assets (fixed income) as the funded status of the plans increase above 90% (as measured by the market value of qualified pension plan assets divided by the projected benefit obligations of the qualified pension plans). The asset mix and acceptable minimum and maximum ranges established by the policy for the pension and other postretirement benefit plans are as follows: Asset Mix Policy of Funds: Defined Benefit Pension Plan Postretirement Benefit Plan Asset Category Minimum Maximum Minimum Maximum Domestic Equities 25% 45% 35% 55% International Equities 15% 25% 15% 25% Fixed Income 23% 37% 20% 50% Real Estate/Private Equity/Hedge Funds 0% 15% 0% 0% Short-Term Investments 0% 10% 0% 10% Pension Plan and Postretirement Plan Asset Mix at December 31, 2015 and December 31, 2014 : (in millions) Defined Benefit Pension Assets December 31, Postretirement December 31, Asset Class Asset Value % of Total Assets Asset Value % of Total Assets Domestic Equities $ 686.3 39.3 % $ 105.0 46.5 % International Equities 323.2 18.5 % 39.6 17.5 % Fixed Income 619.3 35.5 % 79.1 35.0 % Real Estate/Private Equity/Hedge Funds 96.7 5.5 % — — Cash/Other 21.6 1.2 % 2.2 1.0 % Total $ 1,747.1 100.0 % $ 225.9 100.0 % (in millions) Defined Benefit Pension Assets December 31, Postretirement Benefit Plan Assets December 31, Asset Class Asset Value % of Total Assets Asset Value % of Total Assets Domestic Equities $ 957.2 41.1 % $ 219.6 47.2 % International Equities 420.5 18.1 % 85.6 18.4 % Fixed Income 802.4 34.4 % 158.6 34.1 % Real Estate/Private Equity/Hedge Funds 117.6 5.0 % — — Cash/Other 32.6 1.4 % 1.2 0.3 % Total $ 2,330.3 100.0 % $ 465.0 100.0 % The categorization of investments into the asset classes in the table above are based on definitions established by the NiSource Benefits Committee. Fair Value Measurements. The following table sets forth, by level within the fair value hierarchy, the Master Trust and other postretirement benefits investment assets at fair value as of December 31, 2015 and 2014 . Assets and liabilities are classified in their entirety based on the lowest level of input that is significant to the fair value measurement. Total Master Trust and other postretirement benefits investment assets at fair value classified within Level 3 were $95.3 million and $117.0 million as of December 31, 2015 and December 31, 2014 , respectively. Such amounts were approximately 5% and 4% of the Master Trust and other postretirement benefits’ total investments as reported on the statement of net assets available for benefits at fair value as of December 31, 2015 and 2014 , respectively. Valuation Techniques Used to Determine Fair Value: Level 1 Measurements Most common and preferred stocks are traded in active markets on national and international securities exchanges and are valued at closing prices on the last business day of each period presented. Cash is stated at cost which approximates their fair value, with the exception of cash held in foreign currencies which fluctuates with changes in the exchange rates. Short-term bills and notes are priced based on quoted market values. Level 2 Measurements Most U.S. Government Agency obligations, mortgage/asset-backed securities, and corporate fixed income securities are generally valued by benchmarking model-derived prices to quoted market prices and trade data for identical or comparable securities. To the extent that quoted prices are not available, fair value is determined based on a valuation model that includes inputs such as interest rate yield curves and credit spreads. Securities traded in markets that are not considered active are valued based on quoted market prices, broker or dealer quotations, or alternative pricing sources with reasonable levels of price transparency. Other fixed income includes futures and options which are priced on bid valuation or settlement pricing. Commingled funds that hold underlying investments that have prices which are derived from the quoted prices in active markets are classified as Level 2. The funds' underlying assets are principally marketable equity and fixed income securities. Units held in commingled funds are valued at the unit value as reported by the investment managers. The fair value of the investments in commingled funds has been estimated using the net asset value per share of the investments. Level 3 Measurements Commingled funds that hold underlying investments that have prices which are not derived from the quoted prices in active markets are classified as Level 3. The respective fair values of these investments are determined by reference to the funds' underlying assets, which are principally marketable equity and fixed income securities. Units held in commingled funds are valued at the unit value as reported by the investment managers. These investments are often valued by investment managers on a periodic basis using pricing models that use market, income, and cost valuation methods. Private equity investment strategies include buy-out, venture capital, growth equity, distressed debt, and mezzanine debt. Private equity investments are held through limited partnerships. Limited partnerships are valued at estimated fair market value based on their proportionate share of the partnership's fair value as recorded in the partnerships' audited financial statements. Partnership interests represent ownership interests in private equity funds and real estate funds. Real estate partnerships invest in natural resources, commercial real estate and distressed real estate. The fair value of these investments is determined by reference to the funds' underlying assets, which are principally securities, private businesses, and real estate properties. The value of interests held in limited partnerships, other than securities, is determined by the general partner, based upon third-party appraisals of the underlying assets, which include inputs such as cost, operating results, discounted cash flows and market based comparable data. Private equity and real estate limited partnerships typically call capital over a three to five year period and pay out distributions as the underlying investments are liquidated. The typical expected life of these limited partnerships is 10-15 years and these investments typically cannot be redeemed prior to liquidation. For the year ended December 31, 2015 , there were no significant changes to valuation techniques to determine the fair value of NiSource's pension and other postretirement benefits' assets. Fair Value Measurements at December 31, 2015 : (in millions) December 31, Quoted Prices in Active Significant Other Significant Pension plan assets: Cash $ 7.0 $ 7.0 $ — $ — Equity securities International equities 45.3 45.3 — — Fixed income securities Government 64.6 — 64.6 — Corporate 95.8 — 95.8 — Other fixed income 0.1 — — 0.1 Mutual Funds U.S. multi-strategy 257.1 257.1 — — International equities 64.9 64.9 — — Fixed income 150.5 150.5 — — Private equity limited partnerships U.S. multi-strategy (1) 46.4 — — 46.4 International multi-strategy (2) 29.3 — — 29.3 Distressed opportunities 5.9 — — 5.9 Real estate 13.6 — — 13.6 Commingled funds Short-term money markets (3) 22.9 U.S. equities (3) 429.2 International equities (3) 210.1 Fixed income (3) 302.5 Pension plan assets subtotal 1,745.2 524.8 160.4 95.3 Other postretirement benefit plan assets: Mutual funds U.S. equities 89.8 89.8 — — International equities 41.4 41.4 — — Fixed income 78.0 78.0 — — Commingled funds Short-term money markets (3) 2.4 U.S. equities (3) 14.3 Other postretirement benefit plan assets subtotal 225.9 209.2 — — Due to brokers, net (4) (0.2 ) Receivables/payables 2.1 Total pension and other post-retirement benefit plan assets $ 1,973.0 $ 734.0 $ 160.4 $ 95.3 (1) This class includes limited partnerships/fund of funds that invest in a diverse portfolio of private equity strategies, including buy-outs, venture capital, growth capital, special situations and secondary markets, primarily inside the United States. (2) This class includes limited partnerships/fund of funds that invest in diverse portfolio of private equity strategies, including buy-outs, venture capital, growth capital, special situations and secondary markets, primarily outside the United States. (3) This class of investments is measured at fair value using the net asset value per share and has not been classified in the fair value hierarchy. (4) This class represents pending trades with brokers. The table below sets forth a summary of changes in the fair value of the Plan’s Level 3 assets for the year ended December 31, 2015 : Balance at January 1, 2015 Total gains or losses (unrealized / realized) Purchases (Sales) Transfers into/(out of) level 3 Balance at December 31, 2015 Fixed income securities Other fixed income $ 0.6 $ — $ — $ (0.5 ) $ — $ 0.1 Private equity limited partnerships U.S. multi-strategy 56.2 (3.5 ) 1.1 (7.4 ) — 46.4 International multi-strategy 35.3 (2.3 ) 0.1 (3.8 ) — 29.3 Distressed opportunities 7.6 (0.5 ) — (1.2 ) — 5.9 Real estate 17.3 (0.5 ) 0.1 (3.3 ) — 13.6 Total $ 117.0 $ (6.8 ) $ 1.3 $ (16.2 ) $ — $ 95.3 The table below sets forth a summary of unfunded commitments, redemption frequency and redemption notice periods for certain investments that are measured at fair value using the net asset value per share for the year ended December 31, 2015 : (in millions) Fair Value Unfunded Commitments Redemption Frequency Redemption Notice Period Commingled Funds Short-term money markets $ 25.3 $ — Daily 1 day U.S. equities 443.5 — Monthly 3 days International equities 210.1 — Monthly 14-30 days Fixed income 302.5 — Monthly 3 days Total $ 981.4 $ — Fair Value Measurements at December 31, 2014 : (in millions) December 31, Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Significant Pension plan assets: Cash $ 17.1 $ 17.1 $ — $ — Equity securities U.S. equities 0.4 0.4 — — International equities 134.5 133.9 0.6 — Fixed income securities Government 118.4 104.6 13.8 — Corporate 257.0 — 257.0 — Mortgages/Asset backed securities 2.7 — 2.7 — Other fixed income 0.6 — — 0.6 Private equity limited partnerships U.S. multi-strategy (1) 56.2 — — 56.2 International multi-strategy (2) 35.3 — — 35.3 Distressed opportunities 7.6 — — 7.6 Real Estate 17.3 — — 17.3 Commingled funds Short-term money markets (3) 32.6 U.S. equities (3) 957.2 International equities (3) 279.9 Fixed income (3) 409.0 Pension plan assets subtotal 2,325.8 256.0 274.1 117.0 Other postretirement benefit plan assets: Mutual funds U.S. equities 189.8 189.8 — — International equities 85.6 85.6 — — Fixed income 158.2 158.2 — — Commingled funds Short-term money markets (3) 1.6 U.S. equities (3) 29.8 Other postretirement benefit plan assets subtotal 465.0 433.6 — — Due to brokers, net (4) (0.6 ) Accrued investment income/dividends 4.6 Receivables/payables 0.5 Total pension and other post-retirement benefit plan assets $ 2,795.3 $ 689.6 $ 274.1 $ 117.0 (1) This class includes limited partnerships/fund of funds that invest in a diverse portfolio of private equity strategies, including buy-outs, venture capital, growth capital, special situations and secondary markets, primarily in the United States. (2) This class includes limited partnerships/fund of funds that invest in a diverse portfolio of private equity strategies, including buy-outs, venture capital, growth capital, special situations and secondary markets, primarily outside the United States. (3) This class of investments is measured at fair value using the net asset value per share and has not been classified in the fair value hierarchy. (4) This class represents pending trades with brokers. The table below sets forth a summary of changes in the fair value of the Plan’s Level 3 assets for the year ended December 31, 2014 : Balance at January 1, 2014 Total gains or losses (unrealized / realized) Purchases (Sales) Transfers into/(out of) level 3 Balance at December 31, 2014 Fixed income securities Mortgages/Asset backed securities $ 0.1 $ — $ — $ (0.1 ) $ — $ — Other fixed income — 0.3 0.3 — — 0.6 Private equity limited partnerships U.S. multi-strategy 57.9 2.7 2.5 (6.9 ) — 56.2 International multi-strategy 38.2 (0.4 ) 0.5 (3.0 ) — 35.3 Distress opportunities 8.9 0.5 0.1 (1.9 ) — 7.6 Real estate 19.6 2.3 0.1 (4.7 ) — 17.3 Total $ 124.7 $ 5.4 $ 3.5 $ (16.6 ) $ — $ 117.0 The table below sets forth a summary of unfunded commitments, redemption frequency and redemption notice periods for certain investments that are measured at fair value using the net asset value per share for the year ended December 31, 2014 : (in millions) Fair Value Unfunded Commitments Redemption Frequency Redemption Notice Period Commingled Funds Short-term money markets $ 34.2 $ — Daily 1 day U.S. equities 987.0 — Monthly 3 days International equities 279.9 — Monthly 14-30 days Fixed income 409.0 — Monthly 3 days Total $ 1,710.1 $ — NiSource Pension and Other Postretirement Benefit Plans’ Funded Status and Related Disclosure . The following table provides a reconciliation of the plans’ funded status and amounts reflected in NiSource’s Consolidated Balance Sheets at December 31 based on a December 31 measurement date: Pension Benefits Other Postretirement Benefits (in millions) 2015 2014 2015 2014 Change in projected benefit obligation (1) Benefit obligation at beginning of year $ 2,751.4 $ 2,528.2 $ 716.0 $ 714.2 Service cost 34.8 34.8 6.4 8.5 Interest cost 95.9 109.0 24.9 30.1 Plan participants’ contributions — — 7.3 9.1 Plan amendments — 0.6 0.1 (41.5 ) Actuarial loss (gain) (91.7 ) 272.1 (71.5 ) 47.6 Settlement loss 0.5 — — — Benefits paid (171.8 ) (193.3 ) (43.7 ) (53.7 ) Estimated benefits paid by incurred subsidy — — 0.8 1.7 Separation of CPG (Note 3) (412.4 ) — (114.5 ) — Projected benefit obligation at end of year $ 2,206.7 $ 2,751.4 $ 525.8 $ 716.0 Change in plan assets Fair value of plan assets at beginning of year $ 2,330.3 $ 2,267.3 $ 465.0 $ 454.2 Actual return on plan assets (49.7 ) 200.4 1.9 20.3 Employer contributions 2.7 55.9 25.8 35.1 Plan participants’ contributions — — 7.3 9.1 Benefits paid (171.8 ) (193.3 ) (43.7 ) (53.7 ) Separation of CPG (Note 3) (364.4 ) — (230.4 ) — Fair value of plan assets at end of year $ 1,747.1 $ 2,330.3 $ 225.9 $ 465.0 Funded Status at end of year $ (459.6 ) $ (421.1 ) $ (299.9 ) $ (251.0 ) Amounts recognized in the statement of financial position consist of: Current liabilities (3.0 ) (3.5 ) (0.6 ) (0.6 ) Noncurrent liabilities (456.6 ) (417.6 ) (299.3 ) (250.4 ) Net amount recognized at end of year (2) $ (459.6 ) $ (421.1 ) $ (299.9 ) $ (251.0 ) Amounts recognized in accumulated other comprehensive income or regulatory asset/liability (3) Unrecognized prior service credit $ 0.7 $ (3.5 ) $ (41.6 ) $ (49.2 ) Unrecognized actuarial loss 925.6 1,009.8 66.1 95.5 $ 926.3 $ 1,006.3 $ 24.5 $ 46.3 (1) The change in benefit obligation for Pension Benefits represents the change in Projected Benefit Obligation while the change in benefit obligation for Other Postretirement Benefits represents the change in Accumulated Postretirement Benefit Obligation. (2) NiSource recognizes in its Consolidated Balance Sheets the underfunded and overfunded status of its various defined benefit postretirement plans, measured as the difference between the fair value of the plan assets and the benefit obligation. (3) NiSource determined that for certain rate-regulated subsidiaries the future recovery of pension and other postretirement benefits costs is probable. These rate-regulated subsidiaries recorded regulatory assets and liabilities of $928.7 million and $8.1 million , respectively, as of December 31, 2015 , and $910.3 million and $10.1 million , respectively, as of December 31, 2014 that would otherwise have been recorded to accumulated other comprehensive loss. NiSource’s accumulated benefit obligation for its pension plans was $2,190.5 million and $2,732.3 million as of December 31, 2015 and 2014 , respectively. The accumulated benefit obligation as of a date is the actuarial present value of benefits attributed by the pension benefit formula to employee service rendered prior to that date and based on current and past compensation levels. The accumulated benefit obligation differs from the projected benefit obligation disclosed in the table above in that it includes no assumptions about future compensation levels. NiSource pension plans were underfunded by $459.6 million at December 31, 2015 compared to being underfunded at December 31, 2014 by $421.1 million . The decline in the funded status was due primarily to unfavorable asset returns offset by the adoption of new mortality improvement assumptions released by the Society of Actuaries in 2015 and the separation of CPG's net liability position in the plans. NiSource contributed $2.7 million and $55.9 million to its pension plans in 2015 and 2014 , respectively. NiSource’s funded status for its other postretirement benefit plans decreased by $48.9 million to an underfunded status of $299.9 million primarily due to unfavorable asset returns and the separation of CPG's net asset position in the plans offset by the adoption of new mortality improvement assumptions released by the Society of Actuaries in 2015. NiSource contributed approximately $25.8 million and $35.1 million to its other postretirement benefit plans in 2015 and 2014 , respectively. No amounts of NiSource’s pension or other postretirement benefit plans’ assets are expected to be returned to NiSource or any of its subsidiaries in 2016. The following table provides the key assumptions that were used to calculate the pension and other postretirement benefits obligations for NiSource’s various plans as of December 31: Pension Benefits Other Postretirement Benefits 2015 2014 2015 2014 Weighted-average assumptions to Determine Benefit Obligation Discount Rate 4.24 % 3.81 % 4.33 % 3.94 % Rate of Compensation Increases 4.00 % 4.00 % — — Health Care Trend Rates Trend for Next Year — — 8.41 % 6.90 % Ultimate Trend — — 4.50 % 4.50 % Year Ultimate Trend Reached — — 2022 2021 Assumed health care cost trend rates have a significant effect on the amounts reported for the health care plans. A one-percentage-point change in assumed health care cost trend rates would have the following effects: (in millions) 1% point increase 1% point decrease Effect on service and interest components of net periodic cost $ 1.7 $ (1.5 ) Effect on accumulated postretirement benefit obligation 32.4 (28.0 ) NiSource expects to make contributions of approximately $3.0 million to its pension plans and approximately $22.2 million to its postretirement medical and life plans in 2016 . The following table provides benefits expected to be paid in each of the next five fiscal years, and in the aggregate for the five fiscal years thereafter. The expected benefits are estimated based on the same assumptions used to measure NiSource’s benefit obligation at the end of the year and includes benefits attributable to the estimated future service of employees: (in millions) Pension Benefits Other Federal Year(s) 2016 $ 174.1 $ 34.7 $ 0.9 2017 175.8 35.4 0.9 2018 177.1 36.0 0.9 2019 176.1 36.7 0.9 2020 174.5 37.0 0.9 2021-2025 837.8 181.5 3.6 The following table provides the components of the plans’ net periodic benefits cost for each of the three years ended December 31, 2015 , 2014 and 2013 : Pension Benefits Other Postretirement Benefits (in millions) 2015 2014 2013 2015 2014 2013 Components of Net Periodic Benefit Cost (Income) Service cost $ 34.8 $ 34.8 $ 36.4 $ 6.4 $ 8.5 $ 12.1 Interest cost 95.9 109.0 98.9 24.9 30.1 32.2 Expected return on assets (167.2 ) (181.1 ) (168.1 ) (28.2 ) (36.8 ) (30.3 ) Amortization of transitional obligation — — — — — 0.5 Amortization of prior service cost (credit) 0.1 0.2 0.3 (5.2 ) (4.3 ) (0.7 ) Recognized actuarial loss 59.3 47.5 77.8 3.4 0.4 11.0 Net Periodic Benefit Costs (Income) 22.9 10.4 45.3 1.3 (2.1 ) 24.8 Additional loss recognized due to: Settlement loss 2.5 — 33.4 — — — Total Net Periodic Benefits Cost (Income) $ 25.4 $ 10.4 $ 78.7 $ 1.3 $ (2.1 ) $ 24.8 The following table provides the key assumptions that were used to calculate the net periodic benefits cost for NiSource’s various plans: Pension Benefits Other Postretirement Benefits 2015 2014 2013 2015 2014 2013 Weighted-average Assumptions to Determine Net Periodic Benefit Cost Discount Rate 3.81 % 4.50 % 3.63 % 3.94 % 4.75 % 3.95 % Expected Long-Term Rate of Return on Plan Assets 8.30 % 8.30 % 8.30 % 8.15 % 8.14 % 8.14 % Rate of Compensation Increases 4.00 % 4.00 % 4.00 % — — — NiSource believes it is appropriate to assume an 8.30% and 8.15% rate of return on pension and other postretirement plan assets, respectively, for its calculation of 2015 pension benefits cost. This is primarily based on asset mix and historical rates of return. The following table provides other changes in plan assets and projected benefit obligations recognized in other comprehensive income or regulatory asset or liability: Pension Benefits Other Postretirement Benefits (in millions) 2015 2014 2015 2014 Other Changes in Plan Assets and Projected Benefit Obligations Recognized in Other Comprehensive Income or Regulatory Asset or Liability Net prior service cost (credit) $ — $ 0.6 $ 0.1 $ (41.5 ) Net actuarial loss (gain) 125.7 252.8 (45.2 ) 64.0 Settlements (2.5 ) — — — Less: amortization of prior service cost (credit) (0.1 ) (0.2 ) 5.2 4.3 Less: amortization of net actuarial loss (gain) (59.3 ) (47.5 ) (3.4 ) (0.4 ) Less: Separation of CPG (Note 3) (143.8 ) — 21.5 — Total Recognized in Other Comprehensive Income or Regulatory Asset or Liability $ (80.0 ) $ 205.7 $ (21.8 ) $ 26.4 Amount Recognized in Net Periodic Benefits Cost and Other Comprehensive Income or Regulatory Asset or Liability $ (54.6 ) $ 216.1 $ (20.5 ) $ 24.3 Based on a December 31 measurement date, the net unrecognized actuarial loss, unrecognized prior service cost (credit), and unrecognized transition obligation that will be amortized into net periodic benefit cost during 2016 for the pension plans are $61.2 million , $(0.2) million and zero , respectively, and for other postretirement benefit plans are $3.1 million , $(4.9) million and zero , respectively.

Authorized Classes Of Cumulativ

Authorized Classes Of Cumulative Preferred And Preference Stocks	12 Months Ended
	Dec. 31, 2015
Preferred Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Authorized Classes Of Cumulative Preferred And Preference Stocks	Authorized Classes of Cumulative Preferred and Preference Stocks NiSource has 20,000,000 authorized shares of Preferred Stock with a $0.01 par value, of which 4,000,000 shares are designated Series A Junior Participating Preferred Shares. The authorized classes of par value and no par value cumulative preferred and preference stocks of NIPSCO are as follows: 2,400,000 shares of Cumulative Preferred with a $100 par value; 3,000,000 shares of Cumulative Preferred with no par value; 2,000,000 shares of Cumulative Preference with a $50 par value; and 3,000,000 shares of Cumulative Preference with no par value. As of December 31, 2015 , NiSource and NIPSCO had no preferred shares outstanding.

Common Stock

Common Stock	12 Months Ended
	Dec. 31, 2015
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Common Stock	Common Stock As of December 31, 2015 , NiSource had 400,000,000 authorized shares of common stock with a $0.01 par value. Common Stock Dividend. Holders of shares of NiSource’s common stock are entitled to receive dividends when, as and if declared by the Board out of funds legally available. The policy of the Board has been to declare cash dividends on a quarterly basis payable on or about the 20th day of February, May, August and November. NiSource has paid quarterly common dividends totaling $0.830 , $1.02 and $0.98 per share for the years ended December 31, 2015 , 2014 and 2013 , respectively. At its January 27, 2016 meeting, the Board declared a quarterly common dividend of $0.155 per share, payable on February 19, 2016 to holders of record on February 8, 2016 . NiSource has certain debt covenants which could potentially limit the amount of dividends the Company could pay in order to maintain compliance with these covenants. Refer to Note 14, "Long-Term Debt," for more information. As of December 31, 2015 , these covenants did not restrict the amount of dividends that were available to be paid. Dividend Reinvestment and Stock Purchase Plan. NiSource offers a Dividend Reinvestment and Stock Purchase Plan which allows participants to reinvest dividends and make voluntary cash payments to purchase additional shares of common stock on the open market.

Share-Based Compensation

Share-Based Compensation	12 Months Ended
	Dec. 31, 2015
Share-based Compensation [Abstract]
Share-Based Compensation	Share-Based Compensation The NiSource stockholders originally approved and adopted the NiSource Inc. 2010 Omnibus Incentive Plan (“Omnibus Plan”) at the Annual Meeting of Stockholders held on May 11, 2010. Stockholders re-approved the Omnibus Plan as amended at the Annual Meeting of Stockholders held on May 12, 2015. The Omnibus Plan provides for awards to employees and non-employee directors of incentive and nonqualified stock options, stock appreciation rights, restricted stock, restricted stock units, performance shares, performance units, cash-based awards and other stock-based awards and supersedes the long-term incentive plan approved by stockholders on April 13, 1994 (“1994 Plan”) and the Director Stock Incentive Plan (“Director Plan”). The Omnibus Plan provides that the number of shares of common stock of NiSource available for awards is 8,000,000 plus the number of shares subject to outstanding awards that expire or terminate for any reason that were granted under either the 1994 Plan or the Director Plan, plus the number of shares that were awarded as a result of the Separation-related adjustments described below. At December 31, 2015 , there were 5,704,139 shares reserved for future awards under the Omnibus Plan. NiSource recognized stock-based employee compensation expense of $18.8 million , $29.8 million and $19.6 million , during 2015 , 2014 and 2013 , respectively, as well as related tax benefits of $7.2 million , $11.8 million and $7.8 million , respectively. As of December 31, 2015 , the total remaining unrecognized compensation cost related to nonvested awards amounted to $14.9 million , which will be amortized over the weighted-average remaining requisite service period of 1.7 years. Separation-related Adjustments . In connection with the Separation, NiSource and CPG entered into an Employee Matters Agreement, effective July 1, 2015. Under the terms of the Employee Matters Agreement, and pursuant to the terms of the Omnibus Plan, the Compensation Committee of the Board of NiSource approved an adjustment to outstanding awards granted under the Omnibus Plan in order to preserve the intrinsic aggregate value of such awards before the Separation (the “Valuation Adjustment”). The Separation-related adjustments did not have a material impact on either compensation expense or the potentially dilutive securities to be considered in the calculation of diluted earnings per share of common stock. Former NiSource employees transferred to CPG as a result of the Separation surrendered their outstanding unvested NiSource awards effective July 1, 2015. Restricted Stock Units and Restricted Stock . In 2015 , NiSource granted restricted stock units and shares of restricted stock of 660,230 , subject to service conditions. The total grant date fair value of the shares of restricted stock units and shares of restricted stock was $23.9 million , based on the average market price of NiSource’s common stock at the date of each grant less the present value of any dividends not received during the vesting period, which will be expensed, net of forfeitures, over the vesting period which is generally three years. Including the effect of the Valuation Adjustment, 808,928 of the unvested restricted stock units and shares of restricted stock granted in 2015 remained outstanding as of December 31, 2015 . In 2014 , NiSource granted restricted stock units and shares of restricted stock of 158,633 , subject to service conditions. The total grant date fair value of the restricted stock units and shares of restricted stock was $5.2 million , based on the average market price of NiSource’s common stock at the date of each grant less the present value of any dividends not received during the vesting period, which will be expensed, net of forfeitures, over the vesting period which is generally three years. Including the effect of the Valuation Adjustment, 46,810 of the unvested restricted stock units and shares of restricted stock granted in 2014 remained outstanding as of December 31, 2015 . In 2013 , NiSource granted restricted stock units and shares of restricted stock of 69,651 , subject to service conditions. The total grant date fair value of the restricted stock units and shares of restricted stock was $1.8 million , based on the average market price of NiSource’s common stock at the date of each grant less the present value of any dividends not received during the vesting period, which will be expensed, net of forfeitures, over the vesting period which is generally three years. Including the effect of the Valuation Adjustment, 83,415 of the unvested restricted stock units and shares of restricted stock granted in 2013 remained outstanding as of December 31, 2015 . If an employee terminates employment before the service conditions lapse under the 2013, 2014 and 2015 awards due to (1) Retirement or Disability (as defined in the award agreement), or (2) death, the service conditions will lapse on the date of such termination with respect to a pro rata portion of the restricted stock units and shares of restricted stock based upon the percentage of the service period satisfied between the grant date and the date of the termination of employment. In the event of a Change-in-Control (as defined in the award agreement), all unvested shares of restricted stock and restricted stock units awarded prior to 2014 will immediately vest and all unvested shares of restricted stock and restricted stock units awarded in 2014 and 2015 will immediately vest upon termination of employment occurring in connection with a Change-in-Control. Termination due to any other reason will result in all unvested shares of restricted stock and restricted stock units awarded being forfeited effective on the employee’s date of termination. As a result of the Separation, restricted stock units were substituted for outstanding performance shares awarded in 2013 and 2014 (discussed below), as adjusted based on a modified performance period and modified performance goals, and were subject to the same service based vesting conditions as the performance share awards they replaced. These converted restricted stock unit awards were also subject to the Valuation Adjustment. As of December 31, 2015, 2,190,129 of these restricted stock units remained outstanding. Under these new restricted stock unit agreements, if the employee terminates employment before the service conditions lapse under the 2013 and 2014 awards due to (1) Retirement or Disability (as defined in the award agreement), or (2) death, the employment conditions will lapse with respect to a pro rata portion of the new restricted stock units based upon the percentage of the service period satisfied between the grant date and the date of the termination of employment. In the event of a Change-in-Control (as defined in the award agreement), all new restricted stock units will immediately vest upon termination of employment occurring in connection with a change-in-control. Termination due to any other reason will result in all of the new restricted stock units awarded being forfeited effective on the employee’s date of termination. Restricted Stock Units Weighted Average Grant Date Fair Value ($) (1) Nonvested at December 31, 2014 307,329 27.92 Granted 660,230 36.23 Forfeited (22,860 ) 16.98 Vested (94,380 ) 20.61 Awards surrendered as a result of the Separation (445,123 ) Awards granted in conversion as a result of the Separation 547,148 Nonvested and Expected to Vest 952,344 14.38 Performance Shares Converted to Restricted Stock Units as a result of the Separation 2,190,129 6.01 Nonvested and Expected to Vest at December 31, 2015 3,142,473 8.55 (1) The reduction in weighted average grant date fair value during 2015 primarily resulted from the significant number of incremental units issued as a result of the Separation. As discussed above in "Separation-related Adjustments," these incremental units were issued to preserve the intrinsic value of such awards immediately before the Separation. Performance Shares . In 2015 , NiSource did not grant any performance shares subject to performance and service conditions. In 2014 , NiSource granted 535,037 performance shares subject to performance and service conditions. The grant date fair-value of the awards was $16.6 million , based on the average market price of NiSource’s common stock at the date of each grant less the present value of dividends not received during the vesting period which will be expensed, net of forfeitures, over the three year requisite service period. The performance conditions were based on achievement of cumulative net operating earnings per share, a non-GAAP financial measure that NiSource defines as income from continuing operations adjusted for certain items, for the three-year period ending December 31, 2016; and relative total shareholder return, a non-GAAP market measure that NiSource defines as the annualized growth in the dividends and share price of a share of NiSource’s common stock (calculated using a 20 trading day average of NiSource’s closing price, over a period beginning December 31, 2013 and ending on December 31, 2016) compared to the total shareholder return performance of a predetermined peer group of companies. The service conditions for these awards lapse on February 28, 2017. In 2013 , NiSource granted 664,776 performance shares subject to performance and service conditions. The grant date fair-value of the awards was $15.7 million , based on the average market price of NiSource’s common stock at the date of each grant less the present value of dividends not received during the vesting period which will be expensed, net of forfeitures, over the three year requisite service period. The performance conditions are based on achievement of certain non-GAAP financial measures: cumulative net operating earnings, which NiSource defines as income from continuing operations adjusted for certain items; and cumulative funds from operations, which NiSource defines as net operating cash flows provided by continuing operations, in each case for the three-year period ending December 31, 2015; and relative total shareholder return, a non-GAAP market measure that NiSource defines as the annualized growth in the dividends and share price of a share of NiSource’s common stock (calculated using a 20 trading day average of NiSource’s closing price beginning December 31, 2012 and ending on December 31, 2015) compared to the total shareholder return performance of a predetermined peer group of companies. The service conditions for these awards lapse on February 29, 2016. Performance Awards Weighted Average Grant Date Fair Value ($) Nonvested at December 31, 2014 1,727,855 24.80 Granted — — Forfeited (110,013 ) 9.24 Vested (649,896 ) 20.29 Awards surrendered as a result of the Separation (573,486 ) Awards granted in conversion as a result of the Separation 1,795,669 Performance Shares at July 1, 2015 2,190,129 6.01 Awards Converted to Restricted Stock Units as a result of the Separation (2,190,129 ) Nonvested and Expected to Vest at December 31, 2015 — — Non-employee Director Awards . As of May 11, 2010, awards to non-employee directors may be made only under the Omnibus Plan. Currently, restricted stock units are granted annually to non-employee directors, subject to a non-employee director’s election to defer receipt of such restricted stock unit award. The non-employee director’s restricted stock units vest on the last day of the non-employee director’s annual term corresponding to the year the restricted stock units were awarded subject to special pro-rata vesting rules in the event of Retirement or Disability (as defined in the award agreement), or death. The vested restricted stock units are payable as soon as practicable following vesting except as otherwise provided pursuant to the non-employee director’s election to defer. Certain restricted stock units remain outstanding from the Director Plan. All such awards are fully vested and shall be distributed to the directors upon their separation from the Board. In connection with the Separation, non-employee directors holding vested restricted stock units received one CPG restricted stock unit (settled in common stock of CPG) for each vested NiSource restricted stock unit. Restricted stock units granted to directors in 2015, however, were not yet vested as of the Separation. Accordingly, these restricted stock unit awards were subject to the Valuation Adjustment described in the “Separation-related Adjustments” section above. As of December 31, 2015 , 198,996 restricted stock units are outstanding to non-employee directors under either the Omnibus Plan or the Director Plan. Of this amount, 50,092 restricted stock units are nonvested and expected to vest. 401(k) Match, Profit Sharing and Company Contribution. NiSource has a voluntary 401(k) savings plan covering eligible employees that allows for periodic discretionary matches as a percentage of each participant’s contributions payable in shares of NiSource common stock. NiSource also has a retirement savings plan that provides for discretionary profit sharing contributions payable in shares of NiSource common stock to eligible employees based on earnings results; and eligible exempt employees hired after January 1, 2010 receive a non-elective company contribution of 3% of eligible pay payable in shares of NiSource common stock. For the years ended December 31, 2015 , 2014 and 2013 , NiSource recognized 401(k) match, profit sharing and non-elective contribution expense of $27.4 million , $28.1 million and $21.6 million , respectively. In connection with the Separation, employees participating in the 401(k) plan who were invested in the NiSource common stock investment option received a stock dividend of one share of CPG common stock for each share of NiSource common stock owned by them through the 401(k) plan.

Long-Term Debt

Long-Term Debt	12 Months Ended
	Dec. 31, 2015
Long-term Debt, Current and Noncurrent [Abstract]
Long-Term Debt	Long-Term Debt NiSource Finance is a 100% owned, consolidated finance subsidiary of NiSource that engages in financing activities to raise funds for the business operations of NiSource and its subsidiaries. NiSource Finance was incorporated in March 2000 under the laws of the state of Indiana. Prior to 2000, the function of NiSource Finance was performed by Capital Markets. NiSource Finance obligations are fully and unconditionally guaranteed by NiSource. Consequently, no separate financial statements for NiSource Finance are required to be reported. No NiSource subsidiaries guarantee debt. During 2015, NiSource Finance executed a $750.0 million tender offer on fixed-rate long-term debt, redeemed $230.0 million fixed-rate long-term debt at maturity, settled $1,075.0 million term loans, and entered into two forward starting swap-lock transactions with notional values totaling $1,000.0 million . These transactions are detailed as follows: • Prior to the Separation, CPG closed its placement of $2,750.0 million in aggregate principal amount of its senior notes. Using the proceeds from this offering, CPG made cash payments to NiSource representing the settlement of inter-company borrowings and the payment of a one-time special dividend. In May 2015, using proceeds from the cash payments from CPG, NiSource Finance settled its two bank term loans in the amount of $1,075.0 million and executed a tender offer for $750.0 million consisting of a combination of its 5.25% notes due 2017 , 6.40% notes due 2018 and 4.45% notes due 2021 . In conjunction with the debt retired, NiSource Finance recorded a $97.2 million loss on early extinguishment of long-term debt, primarily attributable to early redemption premiums. • On November 28, 2015, NiSource Finance redeemed $230.0 million of 5.36% senior unsecured notes at maturity. • On December 3, 2015, NiSource Finance entered into a forward starting interest rate swap, with a notional amount of $500.0 million , to hedge the variability in cash flows attributable to changes in the benchmark interest rate during the period from the effective date of the swap to the anticipated date of a forecasted debt issuance in 2017. The forward starting interest rate swap was designated as a cash flow hedge at the time the agreements were executed, whereby any gain or loss recognized from the effective date of the swap to the date the associated debt is issued for the effective portion of the hedge is recorded net of tax in AOCI and amortized as a component of interest expense over the life of the designated debt. If some portion of the hedge becomes ineffective, the associated gain or loss will be recognized in earnings. As of December 31, 2015, no ineffectiveness has been recorded. • On December 4, 2015, NiSource Finance entered into a forward starting interest rate swap, with a notional amount of $500.0 million , to hedge the variability in cash flows attributable to changes in the benchmark interest rate during the period from the effective date of the swap to the anticipated date of a forecasted debt issuance in 2018. The forward starting interest rate swap was designated as a cash flow hedge at the time the agreements were executed, whereby any gain or loss recognized from the effective date of the swap to the date the associated debt is issued for the effective portion of the hedge is recorded net of tax in AOCI and amortized as a component of interest expense over the life of the designated debt. If some portion of the hedge becomes ineffective, the associated gain or loss will be recognized in earnings. As of December 31, 2015, no ineffectiveness has been recorded. During 2014, NiSource Finance negotiated a $ 750.0 million term loan and redeemed $ 500.0 million of long-term debt securities. These transactions are detailed as follows: • On August 20, 2014, NiSource Finance negotiated a $ 750.0 million three -year bank term loan with a syndicate of banks which carries a floating interest rate of BBA LIBOR plus 100 basis points. • On July 15, 2014, NiSource Finance redeemed $ 500.0 million of 5.40% senior unsecured notes at maturity. Contemporaneous with this redemption, $500.0 million of associated fixed-to-floating interest rate swaps expired. In the following table are the outstanding long-term debt maturities at December 31, 2015 . The long-term debt maturities shown below include capital lease obligations and the debt of certain low-income housing real estate investments. NiSource does not guarantee the long-term debt obligations of the low-income housing real estate investments. Year Ending December 31, (in millions) 2016 $ 433.7 2017 362.2 2018 488.9 2019 554.7 2020 563.8 After 4,024.4 Total (1) $ 6,427.7 (1) This amount excludes $45.5 million of unamortized discount, premium and expenses. Unamortized debt expense, premium and discount on long-term debt applicable to outstanding bonds are being amortized over the life of such bonds. Of NiSource’s long-term debt outstanding at December 31, 2015 , $109.0 million was issued by NiSource’s subsidiary, Capital Markets. The financial obligations of Capital Markets are subject to a Support Agreement between NiSource and Capital Markets, under which NiSource has committed to make payments of interest and principal on Capital Markets’ obligations in the event of a failure to pay by Capital Markets. Under the terms of the Support Agreement, in addition to the cash flow from cash dividends paid to NiSource by any of its consolidated subsidiaries, the assets of NiSource, other than the stock and assets of NIPSCO, are available as recourse for the benefit of Capital Markets’ creditors. The carrying value of the NiSource assets, excluding the assets of NIPSCO, was $10.4 billion at December 31, 2015 . NiSource is subject to a financial covenant under its revolving credit facility which requires NiSource to maintain a debt to capitalization ratio that does not exceed 70% . A similar covenant in a 2005 private placement note purchase agreement requires NiSource to maintain a debt to capitalization ratio that does not exceed 75% . As of December 31, 2015 , the ratio was 64% . NiSource is also subject to certain other non-financial covenants under the revolving credit facility. Such covenants include a limitation on the creation or existence of new liens on NiSource’s assets, generally exempting liens on utility assets, purchase money security interests, preexisting security interests and an additional subset of assets equal to $150 million . An asset sale covenant generally restricts the sale, lease and/or transfer of NiSource’s assets to no more than 10% of its consolidated total assets and dispositions for a price not materially less than the fair market value of the assets disposed of that do not impair the ability of NiSource and NiSource Finance to perform obligations under the revolving credit facility, and that, together with all other such dispositions, would not have a material adverse effect. The revolving credit facility also includes a cross-default provision, which triggers an event of default under the credit facility in the event of an uncured payment default relating to any indebtedness of NiSource or any of its subsidiaries in a principal amount of $50 million or more. NiSource’s indentures generally do not contain any financial maintenance covenants. However, NiSource’s indentures are generally subject to cross-default provisions ranging from uncured payment defaults of $5 million to $50 million , and limitations on the incurrence of liens on NiSource’s assets, generally exempting liens on utility assets, purchase money security interests, preexisting security interests and an additional subset of assets capped at 10% of NiSource’s consolidated net tangible assets.

Short-Term Borrowings

Short-Term Borrowings	12 Months Ended
	Dec. 31, 2015
Short-term Debt [Abstract]
Short-Term Borrowings	Short-Term Borrowings NiSource Finance currently maintains a $1.5 billion revolving credit facility with a syndicate of banks led by Barclays Capital with a termination date of July 1, 2020 . The purpose of the facility is to fund ongoing working capital requirements including the provision of liquidity support for NiSource Finance's $1.5 billion commercial paper program, provide for issuance of letters of credit and also for general corporate purposes. At December 31, 2015, NiSource had no outstanding borrowings under this facility. At December 31, 2014, NiSource had $500.0 million outstanding under this facility. NiSource Finance's commercial paper program has a program limit of up to $1.5 billion with a dealer group comprised of Barclays, Citigroup, Credit Suisse and Wells Fargo. At December 31, 2015 , NiSource had $321.4 million of commercial paper outstanding. At December 31, 2014, NiSource had $792.6 million of commercial paper outstanding. As of December 31, 2015 , NiSource had $14.7 million of stand-by letters of credit outstanding all of which were under the revolving credit facility. At December 31, 2014, NiSource had $30.9 million of stand-by letters of credit outstanding, of which $14.7 million were under the revolving credit facility. Transfers of accounts receivable are accounted for as secured borrowings resulting in the recognition of short-term debt on the Consolidated Balance Sheets in the amount of $246.0 million and $284.3 million as of December 31, 2015 and 2014 , respectively. Refer to Note 17, "Transfers of Financial Assets," for additional information. Short-term borrowings were as follows: At December 31, (in millions) 2015 2014 Commercial Paper weighted average interest rate of 1.00 % and 0.82% at December 31, 2015 and 2014, respectively. $ 321.4 $ 792.6 Credit facilities borrowings weighted average interest rate of 1.44% at December 31, 2014. — 500.0 Accounts receivable securitization facility borrowings 246.0 284.3 Total Short-Term Borrowings $ 567.4 $ 1,576.9 Given their turnover is less than 90 days, cash flows related to the borrowings and repayments of the items listed above are presented net in the Statements of Consolidated Cash Flows.

Fair Value

Fair Value	12 Months Ended
	Dec. 31, 2015
Fair Value Disclosures [Abstract]
Fair Value	Fair Value A. Fair Value Measurements Recurring Fair Value Measurements . The following tables present financial assets and liabilities measured and recorded at fair value on NiSource’s Consolidated Balance Sheets on a recurring basis and their level within the fair value hierarchy as of December 31, 2015 and December 31, 2014 : Recurring Fair Value Measurements December 31, 2015 ( in millions ) Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Balance as of December 31, 2015 Assets Price risk management assets: Commodity financial price risk programs $ 0.1 $ — $ — $ 0.1 Available-for-sale securities — 128.7 — 128.7 Total $ 0.1 $ 128.7 $ — $ 128.8 Liabilities Price risk management liabilities: Commodity financial price risk programs $ 14.3 $ — $ 0.2 $ 14.5 Interest rate risk activities — 17.4 — 17.4 Total $ 14.3 $ 17.4 $ 0.2 $ 31.9 Recurring Fair Value Measurements December 31, 2014 ( in millions ) Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Balance as of December 31, 2014 Assets Price risk management assets: Commodity financial price risk programs 0.1 — — 0.1 Available-for-sale securities 28.4 103.5 — 131.9 Total $ 28.5 $ 103.5 $ — $ 132.0 Liabilities Price risk management liabilities: Commodity financial price risk programs $ 14.2 $ — $ 0.1 $ 14.3 Total $ 14.2 $ — $ 0.1 $ 14.3 Price risk management assets and liabilities include NYMEX futures and NYMEX options which are commodity exchange-traded and non-exchange-based derivative contracts. Exchange-traded derivative contracts are based on unadjusted quoted prices in active markets and are classified within Level 1. These financial assets and liabilities are secured with cash on deposit with the exchange; therefore nonperformance risk has not been incorporated into these valuations. Certain non-exchange-traded derivatives are valued using broker or over-the-counter, on-line exchanges. In such cases, these non-exchange-traded derivatives are classified within Level 2. Non-exchange-based derivative instruments include swaps, forwards, and options. In certain instances, these instruments may utilize models to measure fair value. NiSource uses a similar model to value similar instruments. Valuation models utilize various inputs that include quoted prices for similar assets or liabilities in active markets, quoted prices for identical or similar assets or liabilities in markets that are not active, other observable inputs for the asset or liability, and market-corroborated inputs, (i.e., inputs derived principally from or corroborated by observable market data by correlation or other means). Where observable inputs are available for substantially the full term of the asset or liability, the instrument is categorized in Level 2. Certain derivatives trade in less active markets with a lower availability of pricing information and models may be utilized in the valuation. When such inputs have a significant impact on the measurement of fair value, the instrument is categorized in Level 3. Credit risk is considered in the fair value calculation of derivative instruments that are not exchange-traded. Credit exposures are adjusted to reflect collateral agreements which reduce exposures. As of December 31, 2015 and 2014 , there were no material transfers between fair value hierarchies. Additionally there were no changes in the method or significant assumptions used to estimate the fair value of NiSource’s financial instruments. Commodity price risk resulting from derivative activities at NiSource’s rate-regulated subsidiaries is limited, since regulations allow recovery of prudently incurred purchased power, fuel and gas costs through the ratemaking process, including gains or losses on these derivative instruments. If states should explore additional regulatory reform, these subsidiaries may begin providing services without the benefit of the traditional ratemaking process and may be more exposed to commodity price risk. Some of NiSource’s rate-regulated utility subsidiaries offer commodity price risk products to its customers for which derivatives are used to hedge forecasted customer usage under such products. These subsidiaries do not have regulatory recovery orders for these products and are subject to gains and losses recognized in earnings due to hedge ineffectiveness. In December 2015, NiSource Finance entered into two forward starting interest-rate swaps, each hedging the interest rate risk on coupon payments arising from $500.0 million of forecasted issuances of long-term debt in each of 2017 and 2018. The 2017 swap was executed with four counterparties, and the 2018 swap with five counterparties. These swaps have been recorded as price risk management liabilities, and are designated as cash flow hedges. Each period the swap instruments will be measured assuming a hypothetical settlement at that point in time. Upon termination of the swap instruments, NiSource will pay or receive a settlement based on the current market value. Credit risk is considered in the fair value calculation of each interest rate swap. As they are based on observable data and valuations of similar instruments, the interest-rate swaps are categorized in Level 2 in the fair value hierarchy. There was no exchange of premium at the initial date of the swaps, and NiSource can settle the swaps at any time. Available-for-sale securities are investments pledged as collateral for trust accounts related to NiSource’s wholly-owned insurance company. Available-for-sale securities are included within “Other investments” in the Consolidated Balance Sheets. NiSource values corporate and mortgage-backed debt securities using a matrix pricing model that incorporates market-based information. These securities trade less frequently and are classified within Level 2. Total unrealized gains and losses from available-for-sale securities are included in other comprehensive income (loss). The amortized cost, gross unrealized gains and losses and fair value of available-for-sale debt securities at December 31, 2015 and December 31, 2014 were: December 31, 2015 (in millions) Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Available-for-sale debt securities U.S. Treasury securities $ 33.7 $ 0.1 $ (0.3 ) $ 33.5 Corporate/Other bonds 95.7 0.3 (0.8 ) 95.2 Total $ 129.4 $ 0.4 $ (1.1 ) $ 128.7 December 31, 2014 (in millions) Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Available-for-sale debt securities U.S. Treasury securities $ 30.8 $ 0.3 $ (0.2 ) $ 30.9 Corporate/Other bonds 100.6 1.0 (0.6 ) 101.0 Total $ 131.4 $ 1.3 $ (0.8 ) $ 131.9 For the years ended December 31, 2015 , 2014 , and 2013 , the realized gain on sale of available for sale U.S. Treasury debt securities was $ 0.2 million , $ 0.1 million and $ 0.5 million , respectively. For the years ended December 31, 2015 , 2014 , and 2013 , the realized gain on sale of available for sale Corporate/Other bond debt securities was $ 0.2 million , $ 0.4 million , and $ 0.4 million , respectively. The cost of maturities sold is based upon specific identification. At December 31, 2015 , approximately $2.2 million of U.S. Treasury debt securities have maturities of less than a year while the remaining securities have maturities of greater than one year. At December 31, 2015 , approximately $ 6.2 million of Corporate/Other bonds have maturities of less than a year while the remaining securities have maturities of greater than one year. There are no material items in the fair value reconciliation of Level 3 assets and liabilities measured at fair value on a recurring basis for the years ended December 31, 2015 and 2014 . Non-recurring Fair Value Measurements . There were no significant non-recurring fair value measurements recorded during the twelve months ended December 31, 2015 . Other Fair Value Disclosures for Financial Instruments . The carrying amount of cash and cash equivalents, restricted cash, notes receivable, customer deposits and short-term borrowings is a reasonable estimate of fair value due to their liquid or short-term nature. NiSource’s long-term borrowings are recorded at historical amounts. The following methods and assumptions were used to estimate the fair value of each class of financial instruments for which it is practicable to estimate fair value. Long-term debt .The fair values of these securities are estimated based on the quoted market prices for the same or similar securities. Certain premium costs associated with the early settlement of long-term debt are not taken into consideration in determining fair value. These fair value measurements are classified as Level 2 within the fair value hierarchy. For the years ended December 31, 2015 and 2014 , there were no changes in the method or significant assumptions used to estimate the fair value of the financial instruments. The carrying amount and estimated fair values of financial instruments were as follows: At December 31, (in millions) Carrying Amount 2015 Estimated Fair Value 2015 Carrying Amount 2014 Estimated Fair Value 2014 Long-term debt (including current portion) $ 6,382.2 $ 6,975.7 $ 8,418.1 $ 9,505.7

Transfers Of Financial Assets

Transfers Of Financial Assets	12 Months Ended
	Dec. 31, 2015
Transfers and Servicing [Abstract]
Transfers Of Financial Assets	Transfers of Financial Assets Transfers of accounts receivable are accounted for as secured borrowings resulting in the recognition of short-term borrowings on the Consolidated Balance Sheets. The maximum amount of debt that can be recognized related to NiSource’s accounts receivable programs is $515 million . All accounts receivables sold to the purchasers are valued at face value, which approximates fair value due to their short-term nature. The amount of the undivided percentage ownership interest in the accounts receivables sold is determined in part by required loss reserves under the agreements. Below is information about the accounts receivable securitization agreements entered into by NiSource’s subsidiaries. Throughout 2015 and 2014, Columbia of Ohio has been under an agreement to sell, without recourse, substantially all of its trade receivables, as they originate, to CGORC, a wholly-owned subsidiary of Columbia of Ohio. CGORC, in turn, is party to an agreement with BTMU and BNS, under the terms of which it sells an undivided percentage ownership interest in its accounts receivable to commercial paper conduits sponsored by BTMU and BNS. T his agreement was last renewed on October 16, 2015; the current agreement expires on October 15, 2016 and can be further renewed if mutually agreed to by all parties. The maximum seasonal program limit under the terms of the current agreement is $240 million . As of December 31, 2015 , $99.4 million of accounts receivable had been transferred by CGORC. CGORC is a separate corporate entity from NiSource and Columbia of Ohio, with its own separate obligations, and upon a liquidation of CGORC, CGORC’s obligations must be satisfied out of CGORC’s assets prior to any value becoming available to CGORC’s stockholder. Throughout 2015 and 2014, NIPSCO has been under an agreement to sell, without recourse, substantially all of its trade receivables, as they originate, to NARC, a wholly-owned subsidiary of NIPSCO. NARC, in turn, is party to an agreement with PNC and Mizuho under the terms of which it sells an undivided percentage ownership interest in its accounts receivable to PNC and a commercial paper conduit sponsored by Mizuho. This agreement was last renewed on August 26, 2015; the current agreement expires on August 24, 2016 and can be further renewed if mutually agreed to by all parties. The maximum seasonal program limit under the terms of the current agreement is $200 million . As of December 31, 2015 , $111.6 million of accounts receivable had been transferred by NARC. NARC is a separate corporate entity from NiSource and NIPSCO, with its own separate obligations, and upon a liquidation of NARC, NARC’s obligations must be satisfied out of NARC’s assets prior to any value becoming available to NARC’s stockholder. Throughout 2015 and 2014, Columbia of Pennsylvania has been under an agreement to sell, without recourse, substantially all of its trade receivables, as they originate, to CPRC, a wholly-owned subsidiary of Columbia of Pennsylvania. CPRC, in turn, is party to an agreement with BTMU under the terms of which it sells an undivided percentage ownership interest in its accounts receivable to a commercial paper conduit sponsored by BTMU. The agreement with BTMU was last renewed on March 10, 2015, having a current scheduled termination date of March 9, 2016 and can be further renewed if mutually agreed to by both parties. The maximum seasonal program limit under the terms of the agreement is $75 million . As of December 31, 2015 , $35.0 million of accounts receivable had been transferred by CPRC. CPRC is a separate corporate entity from NiSource and Columbia of Pennsylvania, with its own separate obligations, and upon a liquidation of CPRC, CPRC’s obligations must be satisfied out of CPRC’s assets prior to any value becoming available to CPRC’s stockholder. The following table reflects the gross and net receivables transferred as well as short-term borrowings related to the securitization transactions as of December 31, 2015 and 2014 for Columbia of Ohio, NIPSCO and Columbia of Pennsylvania: (in millions) December 31, December 31, Gross Receivables $ 450.8 $ 611.7 Less: Receivables not transferred 204.8 327.4 Net receivables transferred $ 246.0 $ 284.3 Short-term debt due to asset securitization $ 246.0 $ 284.3 During 2015 and 2014 , $38.3 million and $19.2 million was recorded as cash flows from financing activities related to the change in short-term borrowings due to the securitization transactions, respectively. For the years ended December 31, 2015 and 2014 , fees of $2.5 million and $2.9 million associated with the securitization transactions were recorded as interest expense, respectively. Columbia of Ohio, NIPSCO and Columbia of Pennsylvania remain responsible for collecting on the receivables securitized and the receivables cannot be sold to another party.

Other Commitments And Contingen

Other Commitments And Contingencies	12 Months Ended
	Dec. 31, 2015
Commitments and Contingencies Disclosure [Abstract]
Other Commitments And Contingencies	Other Commitments and Contingencies A. Guarantees and Indemnities . As a part of normal business, NiSource and certain subsidiaries enter into various agreements providing financial or performance assurance to third parties on behalf of certain subsidiaries. Such agreements include guarantees and stand-by letters of credit. These agreements are entered into primarily to support or enhance the creditworthiness otherwise attributed to a subsidiary on a stand-alone basis, thereby facilitating the extension of sufficient credit to accomplish the subsidiaries’ intended commercial purposes. At December 31, 2015 , NiSource had issued stand-by letters of credit of approximately $14.7 million for the benefit of third parties. B. Other Legal Proceedings . The Company is party to certain claims and legal proceedings arising in the ordinary course of business, none of which is deemed to be individually material at this time. Due to the inherent uncertainty of litigation, there can be no assurance that the resolution of any particular claim or proceeding would not have a material adverse effect on the Company’s results of operations, financial position or liquidity. If one or more of such matters were decided against the Company, the effects could be material to the Company’s results of operations in the period in which the Company would be required to record or adjust the related liability and could also be material to the Company’s cash flows in the periods the Company would be required to pay such liability. C. Environmental Matters . NiSource operations are subject to environmental statutes and regulations related to air quality, water quality, hazardous waste and solid waste. NiSource believes that it is in substantial compliance with the environmental regulations currently applicable to its operations. It is management's continued intent to address environmental issues in cooperation with regulatory authorities in such a manner as to achieve mutually acceptable compliance plans. However, there can be no assurance that fines and penalties will not be incurred. Management expects a significant portion of environmental assessment and remediation costs to be recoverable through rates for certain NiSource companies. As of December 31, 2015 and 2014 , NiSource had recorded an accrual of approximately $123.2 million and $126.6 million , respectively, to cover environmental remediation at various sites. The current portion of this accrual is included in "Legal and environmental" in the Consolidated Balance Sheets. The noncurrent portion is included in "Other noncurrent liabilities" in the Consolidated Balance Sheets. NiSource accrues for costs associated with environmental remediation obligations when the incurrence of such costs is probable and the amounts can be reasonably estimated. The original estimates for cleanup may differ materially from the amount ultimately expended. The actual future expenditures depend on many factors, including currently enacted laws and regulations, the nature and extent of contamination, the method of cleanup and the availability of cost recovery. These expenditures are not currently estimable at some sites. NiSource periodically adjusts its accrual as information is collected and estimates become more refined. Air The actions listed below could require further reductions in emissions from various emission sources. NiSource will continue to closely monitor developments in these matters. Climate Change . Future legislative and regulatory programs, including implementation of the recently promulgated EPA CPP, could significantly restrict GHG emissions or impose a cost or tax on GHG emissions. Additionally, certain rules that increase methane leak detection and permitting requirements for natural gas facilities could restrict GHG emissions or impose additional costs. The CPP and other federally enacted or proposed GHG reduction measures are subject to numerous legal challenges that could change the way the programs are implemented, and NiSource will carefully monitor all GHG reduction proposals and regulations. In addition to the federal programs, the United States and 194 other countries agreed by consensus to limit GHGs to Nationally Determined Contributions (NDCs) beginning after 2020 in the 2015 United Nations Framework Convention on Climate Change Paris Agreement. The United States has proposed a NDC of a 26% reduction from 2005 levels by 2025, a figure that cannot be met with the CPP alone. National Ambient Air Quality Standards . The CAA requires the EPA to set NAAQS for particulate matter and five other pollutants considered harmful to public health and the environment. Periodically, the EPA imposes new, or modifies existing, NAAQS. States that contain areas that do not meet the new or revised standards or contribute significantly to nonattainment of downwind states may be required to take steps to achieve and maintain compliance with the standards. These steps could include additional pollution controls on boilers, engines, turbines and other facilities owned by electric generation and gas distribution operations. The following NAAQS were recently added or modified: Ozone: On October 26, 2015, the EPA issued a final rule to lower the 8-hour ozone standard from 75 ppb to 70 ppb. After the EPA proceeds with designations, areas where NiSource operates that are currently designated in attainment with the standards may be re-classified as nonattainment. NiSource will continue to monitor this matter and cannot estimate its impact at this time. Waste NiSource subsidiaries are potentially responsible parties at waste disposal sites under the CERCLA (commonly known as Superfund) and similar state laws. Additionally, NiSource affiliates have retained environmental liabilities, including cleanup liabilities, associated with certain former operations. A program has been instituted to identify and investigate former MGP sites where Gas Distribution Operations subsidiaries or predecessors may have liability. The program has identified 64 such sites where liability is probable. Remedial actions at many of these sites are being overseen by state or federal environmental agencies through consent agreements or voluntary remediation agreements. NiSource utilizes a probabilistic model to estimate its future remediation costs related to its MGP sites. The model was prepared with the assistance of a third-party and incorporates NiSource and general industry experience with remediating MGP sites. NiSource completes an annual refresh of the model in the second quarter of each fiscal year. No material changes to the estimated future remediation costs were noted as a result of the refresh completed as of June 30, 2015. The total estimated liability at NiSource related to the facilities subject to remediation was $110.4 million and $121.5 million at December 31, 2015 and 2014 , respectively. The liability represents NiSource’s best estimate of the probable cost to remediate the facilities. NiSource believes that it is reasonably possible that remediation costs could vary by as much as $25 million in addition to the costs noted above. Remediation costs are estimated based on the best available information, applicable remediation standards at the balance sheet date, and experience with similar facilities. Additional Issues Related to Individual Business Segments The sections below describe various regulatory actions that affect individual business segments for which NiSource has retained a liability. Electric Operations. Air NIPSCO is subject to a number of air-quality mandates in the next several years. The mandates, which include the NSR Consent Decree, the Utility Mercury and Air Toxics Standards Rule (MATS), and the CPP, require or may require NIPSCO to make capital improvements to its electric generating stations. The cost of capital improvements associated with the NSR Consent Decree and MATS is estimated to be $860 million , of which approximately $28.8 million remains to be spent. The cost to comply with the CPP cannot be estimated at this time. NIPSCO believes that the capital costs associated with these air quality mandates are likely recoverable through rates. Utility Mercury and Air Toxics Standards Rule: On February 16, 2012, the EPA issued the MATS rule establishing new emissions limits for mercury and other air toxics. Certain affected NIPSCO units have completed projects to meet the April 2015 compliance deadline. For NIPSCO’s remaining affected units, a one-year compliance extension granted by IDEM delays the compliance date until April 2016. NIPSCO continues to implement an IURC-approved plan for the installation of additional environmental controls needed to comply with the MATS extension. On June 29, 2015, the United States Supreme Court remanded the MATS rule back to the United States Court of Appeals for the District of Columbia Circuit for further proceedings. On December 15, 2015, the United States Court of Appeals for the District of Columbia Circuit issued an order remanding the MATS rule to the EPA without vacating the rule. The MATS rule remains in effect while the EPA addresses the issues raised by the United State Supreme Court. The EPA indicates that these issues will be fully addressed by April 15, 2016. NIPSCO will continue to monitor developments in this matter. Clean Power Plan : On October 23, 2015, the EPA issued a final rule to regulate CO 2 emissions from existing fossil-fuel EGUs under section 111(d) of the CAA. The final rule establishes national CO 2 emission-rate standards that are applied to each state’s mix of affected EGUs to establish state-specific emission-rate and mass-emission limits. The final rule requires each state to submit a plan indicating how the state will meet the EPA's emission-rate or mass-emission limit, including possibly imposing reduction obligations on specific units. If a state does not submit a satisfactory plan, the EPA will impose a federal plan on that state. On February 9, 2016, the U.S. Supreme Court stayed implementation of the CPP until litigation is decided on its merits. The cost to comply with this rule will depend on a number of factors, including the outcome of CPP litigation, the requirements of the state plan or final federal plan, and the level of NIPSCO's required CO 2 emission reductions. It is possible that this new rule, comprehensive federal or state GHG legislation, or other GHG regulation could result in additional expense or compliance costs that could materially impact NiSource's financial results. NIPSCO will continue to monitor this matter and cannot estimate its impact at this time. Cross State Air Pollution Rule: On December 3, 2015, the EPA issued a proposed rule to address interstate air quality impacts associated with the 2008 ozone NAAQS and also in response to a court mandate requiring the recalculation of downwind contributions of NOx to states’ abilities to meet the ozone NAAQS. Under the proposed recalculation, NIPSCO may be required to meet a more stringent NOx emission allocation associated with its already well-controlled units. NIPSCO will continue to monitor this matter and cannot estimate its impact at this time. Water On August 15, 2014, the EPA issued the final Phase II Rule of the Clean Water Act Section 316(b), which requires all large existing steam electric generating stations to meet certain performance standards to reduce the effects on aquatic organisms at their cooling water intake structures. Under this rule, stations will have to either demonstrate that the performance of their existing fish protection systems meet the new standards or develop new systems, such as a closed-cycle cooling tower. The cost to comply will depend on a number of factors, including evaluation of the various compliance options available under the regulation and permitting-related determinations by IDEM. NIPSCO estimates that the cost of compliance is between $4 million and $35 million , dependent upon study results, agency requirements and technology ultimately required to achieve compliance. On November 3, 2015, the EPA issued a final rule to amend the effluent limitations guidelines and standards for the Steam Electric Power Generating category. The final rule became effective January 4, 2016. The rule imposes new water treatment and discharge requirements on NIPSCO's electric generating facilities to be applied between 2018-2023. NIPSCO is currently reviewing the rule and cannot estimate the cost of compliance at this time. Waste On April 17, 2015, the EPA issued a final rule for regulation of CCRs. The rule regulates CCRs under the Resource Conservation and Recovery Act Subtitle D, which determines them to be nonhazardous. The rule will require increased groundwater monitoring, reporting, record keeping and posting of related information to the Internet. The rule also establishes requirements related to CCR management, impoundments, landfills and storage. The rule will allow NIPSCO to continue its byproduct beneficial use program. The publication of the CCR rule resulted in revisions to previously recorded legal obligations associated with the retirement of certain NIPSCO facilities. The actual asset retirement costs related to the CCR rule may vary substantially from the estimates used to record the increased asset retirement obligation due to the uncertainty about the compliance strategies that will be used and the preliminary nature of available data used to estimate costs. Refer to Note 6, "Asset Retirement Obligations," for further information. In addition, to comply with the rule, NIPSCO will be required to incur future capital expenditures to modify its infrastructure and manage CCRs. Based upon a preliminary engineering study, capital compliance costs are currently expected to be in the $100 million to $220 million range. As allowed by the EPA, NIPSCO will continue to collect data over time to determine the specific compliance solutions and associated costs and, as a result, the actual costs may vary. NIPSCO believes that the costs associated with CCR compliance are likely recoverable through rates. D. Operating and Capital Lease Commitments. NiSource leases assets in several areas of its operations. Payments made in connection with operating leases were $ 47.5 million in 2015 , $ 59.8 million in 2014 and $ 47.2 million in 2013 , and are primarily charged to operation and maintenance expense as incurred. Capital lease assets and related accumulated depreciation included in the Consolidated Balance Sheets were $ 236.2 million and $ 44.0 million at December 31, 2015 , and $ 286.8 million and $ 86.0 million at December 31, 2014 , respectively. NIPSCO has a service agreement with Pure Air, a general partnership between Air Products and Chemicals, Inc. and First Air Partners LP, under which Pure Air provides scrubber services to reduce sulfur dioxide emissions for Units 7 and 8 at the Bailly Generating Station. Services under this contract commenced on July 1, 1992 and expired on June 30, 2012. The agreement was renewed effective July 1, 2012 for ten years and NIPSCO will continue to pay for the services under a combination of fixed and variable charges. In accordance with GAAP, the renewed agreement was evaluated to determine whether the arrangement qualified as a lease. Based on the terms of the agreement, the arrangement qualified for capital lease accounting. As the effective date of the new agreement was July 1, 2012, NiSource capitalized this lease beginning in the third quarter of 2012. Future minimum rental payments required under operating and capital leases that have initial or remaining non-cancelable lease terms in excess of one year are: (in millions) Operating Leases (1) Capital Leases (2) 2016 $ 18.4 $ 23.5 2017 11.1 23.0 2018 8.8 23.3 2019 7.0 23.7 2020 3.5 23.5 After 13.3 196.3 Total future minimum payments $ 62.1 $ 313.3 (1) Operating lease balances do not include amounts for fleet leases that can be renewed beyond the initial lease term. The Company anticipates renewing the leases beyond the initial term, but the anticipated payments associated with the renewals do not meet the definition of expected minimum lease payments and therefore are not included above. Expected payments are $30.5 million in 2016, $30.9 million in 2017, $26.7 million in 2018, $20.3 million in 2019, $12.5 million in 2020 and $7.5 million thereafter. (2) Capital lease payments shown above are inclusive of interest totaling $114.7 million . E. Purchase and Service Obligations . NiSource has entered into various purchase and service agreements whereby NiSource is contractually obligated to make certain minimum payments in future periods. NiSource’s purchase obligations are for the purchase of physical quantities of natural gas, electricity and coal. NiSource’s service agreements encompass a broad range of business support and maintenance functions which are generally described below. NiSource’s subsidiaries have entered into various energy commodity contracts to purchase physical quantities of natural gas, electricity and coal. These amounts represent minimum quantities of these commodities NiSource is obligated to purchase at both fixed and variable prices. In July 2008, the IURC issued an order approving NIPSCO’s purchase power agreements with subsidiaries of Iberdrola Renewables, Buffalo Ridge I LLC and Barton Windpower LLC. These agreements provide NIPSCO the opportunity and obligation to purchase up to 100 mw of wind power generated commencing in early 2009. The contracts extend 15 and 20 years, representing 50 mw of wind power each. No minimum quantities are specified within these agreements due to the variability of electricity generation from wind, so no amounts related to these contracts are included in the table below. Upon any termination of the agreements by NIPSCO for any reason (other than material breach by Buffalo Ridge I LLC or Barton Windpower LLC), NIPSCO may be required to pay a termination charge that could be material depending on the events giving rise to termination and the timing of the termination. NIPSCO began purchasing wind power in April 2009. NiSource has pipeline service agreements that provide for pipeline capacity, transportation and storage services. These agreements, which have expiration dates ranging from 2016 to 2045 , require NiSource to pay fixed monthly charges. The amounts in the table below include agreements with CPG. Beginning July 1, 2015, these agreements represent third-party transactions and are not eliminated in consolidation. On December 31, 2013, NiSource Corporate Services signed a seven year agreement with IBM to continue to provide business process and support functions to NiSource under a combination of fixed or variable charges, with the variable charges fluctuating based on the actual need for such services. The agreement was effective January 1, 2014 with a commencement date of April 1, 2014 and includes some targeted service enhancements as well as continued existing information technology support services and a few additional support services. On June 15, 2015, NiSource Corporate Services signed an Amendment to this agreement to incorporate changes in services related to the Separation. Refer to Note 3, "Discontinued Operations," in the notes to the Consolidated Financial Statements for additional information on the Separation. Under the amended agreement, at December 31, 2015, NiSource Corporate Services expects to pay approximately $410.1 million to IBM in service and project fees as shown in the table below. Upon any termination of the agreement by NiSource for any reason (other than material breach by IBM), NiSource may be required to pay IBM a termination charge that could include a breakage fee, repayment of IBM's capital investments not yet recovered and IBM's wind-down expense. This termination fee could be material depending on the events giving rise to the termination and the timing of the termination. NIPSCO has contracts with three major rail operators providing for coal transportation services for which there are certain minimum payments. These service contracts extend for various periods through 2018 . The estimated aggregate amounts of minimum fixed payments at December 31, 2015 , were: (in millions) Energy Commodity Agreements Pipeline Service Agreements IBM Service Agreement Other Service Agreements Total 2016 $ 169.3 $ 512.7 $ 90.9 $ 72.0 $ 844.9 2017 74.8 496.0 82.8 67.2 720.8 2018 67.5 341.0 80.1 19.7 508.3 2019 70.6 245.4 78.6 4.6 399.2 2020 72.6 139.3 77.7 2.3 291.9 After 0.4 429.9 — — 430.3 Total purchase and service obligations $ 455.2 $ 2,164.3 $ 410.1 $ 165.8 $ 3,195.4 F. Other Matters. Transmission Upgrade Agreements. On February 11, 2014, NIPSCO entered into TUAs with upgrade sponsors to complete upgrades on NIPSCO’s transmission system on behalf of those sponsors. The upgrade sponsors agreed to reimburse NIPSCO for the total cost to construct transmission upgrades and place them into service, multiplied by a rate of 1.71 ("the multiplier"). On June 10, 2014, certain upgrade sponsors for both TUAs filed a complaint at the FERC against NIPSCO regarding the multiplier stated in the TUAs. On June 30, 2014, NIPSCO filed an answer defending the terms of the TUAs and the just and reasonable nature of the multiplier charged therein and moved for dismissal of the complaint. On December 8, 2014, the FERC issued an order in response to the complaint finding that it is appropriate for NIPSCO to recover, through the multiplier, substantiated costs of ownership related to the TUAs. The FERC set for hearing the issue of what constitutes the incremental costs NIPSCO will incur, but is holding that hearing in abeyance to allow for settlement. NIPSCO will continue to monitor developments in this matter and does not believe the impact is material to the Consolidated Financial Statements. Springfield, Massachusetts. On November 23, 2012, while Columbia of Massachusetts was investigating the source of an odor of gas at a service location in Springfield, Massachusetts, a gas service line was pierced and an explosion occurred. While this explosion impacted multiple buildings and resulted in several injuries, no life threatening injuries or fatalities have been reported. Columbia of Massachusetts fully cooperated with both the Massachusetts DPU and the Occupational Safety & Health Administration in their investigations of this incident, which have been concluded. Columbia of Massachusetts believes any costs associated with damages, injuries and other losses related to this incident are substantially covered by insurance. Any amounts not covered by insurance are not expected to have a material impact on NiSource's consolidated financial statements. In accordance with GAAP, NiSource recorded any accruals and the related insurance recoveries resulting from this incident on a gross basis within the Consolidated Balance Sheets.

Accumulated Other Comprehensive

Accumulated Other Comprehensive Loss	12 Months Ended
	Dec. 31, 2015
Components of Accumulated Other Comprehensive Income (Loss) [Abstract]
Accumulated Other Comprehensive Loss	Accumulated Other Comprehensive Loss The following table displays the activity of Accumulated Other Comprehensive Loss, net of tax: (in millions) Gains and Losses on Securities (1) Gains and Losses on Cash Flow Hedges (1) Pension and OPEB Items (1) Accumulated Other Comprehensive Loss (1) Balance as of January 1, 2013 $ 2.6 $ (28.6 ) $ (39.5 ) $ (65.5 ) Other comprehensive income before reclassifications (2.4 ) 0.1 17.8 15.5 Amounts reclassified from accumulated other comprehensive income (0.5 ) 2.7 4.2 6.4 Net current-period other comprehensive income (loss) (2.9 ) 2.8 22.0 21.9 Balance as of December 31, 2013 $ (0.3 ) $ (25.8 ) $ (17.5 ) $ (43.6 ) Other comprehensive income before reclassifications 0.9 (0.3 ) (10.2 ) (9.6 ) Amounts reclassified from accumulated other comprehensive income (0.3 ) 2.5 0.4 2.6 Net current-period other comprehensive income (loss) 0.6 2.2 (9.8 ) (7.0 ) Balance as of December 31, 2014 $ 0.3 $ (23.6 ) $ (27.3 ) $ (50.6 ) Other comprehensive income before reclassifications (0.5 ) (11.0 ) (5.0 ) (16.5 ) Amounts reclassified from accumulated other comprehensive income (0.3 ) 3.2 2.6 5.5 Net current-period other comprehensive income (loss) (0.8 ) (7.8 ) (2.4 ) (11.0 ) Allocation of AOCI to noncontrolling interest — 2.0 — 2.0 Distribution of CPG to shareholders (Note 3) — 13.9 10.6 24.5 Balance as of December 31, 2015 $ (0.5 ) $ (15.5 ) $ (19.1 ) $ (35.1 ) (1) All amounts are net of tax. Amounts in parentheses indicate debits.

Other, Net

Other, Net	12 Months Ended
	Dec. 31, 2015
Other Nonoperating Income (Expense) [Abstract]
Other, Net	Other, Net Year Ended December 31, (in millions) 2015 2014 2013 Interest Income $ 0.8 $ 3.8 $ 3.5 AFUDC Equity 11.5 10.7 11.7 Charitable Contributions (4.8 ) (11.1 ) (8.2 ) Miscellaneous (1) 9.9 10.0 (0.2 ) Total Other, net $ 17.4 $ 13.4 $ 6.8 (1) Miscellaneous primarily consists of transmission upgrade agreement income in 2015 and 2014.

Interest Expense, Net

Interest Expense, Net	12 Months Ended
	Dec. 31, 2015
Interest Expense [Abstract]
Interest Expense, Net	Interest Expense, Net Year Ended December 31, (in millions) 2015 2014 2013 Interest on long-term debt $ 377.5 $ 368.6 $ 364.4 Interest on short-term borrowings (1) 2.2 5.2 2.7 Debt discount/cost amortization 8.7 8.0 7.5 Accounts receivable securitization 2.5 2.9 2.7 Allowance for borrowed funds used and interest capitalized during construction (5.4 ) (5.3 ) (6.1 ) Other (5.3 ) 0.1 4.1 Total Interest Expense, net $ 380.2 $ 379.5 $ 375.3 (1) Refer to Note 15, "Short-Term Borrowings," for additional information.

Segments Of Business

Segments Of Business	12 Months Ended
	Dec. 31, 2015
Segment Reporting [Abstract]
Segments Of Business	Segments of Business At December 31, 2015 , NiSource’s operations are divided into two primary reportable segments. The Gas Distribution Operations segment provides natural gas service and transportation for residential, commercial and industrial customers in Ohio, Pennsylvania, Virginia, Kentucky, Maryland, Indiana and Massachusetts. The Electric Operations segment provides electric service in 20 counties in the northern part of Indiana. On July 1, 2015, NiSource completed the Separation. CPG's operations consisted of all of NiSource's former Columbia Pipeline Group Operations segment prior to the Separation. Results of the Columbia Pipeline Group Operations segment are included in discontinued operations. The following table provides information about business segments. NiSource uses operating income as its primary measurement for each of the reported segments and makes decisions on finance, dividends and taxes at the corporate level on a consolidated basis. Segment revenues include intersegment sales to affiliated subsidiaries, which are eliminated in consolidation. Affiliated sales are recognized on the basis of prevailing market, regulated prices or at levels provided for under contractual agreements. Operating income is derived from revenues and expenses directly associated with each segment. Year Ended December 31, (in millions) 2015 2014 2013 REVENUES Gas Distribution Operations Unaffiliated $ 3,068.7 $ 3,593.6 $ 3,053.5 Intersegment 0.4 0.3 0.3 Total 3,069.1 3,593.9 3,053.8 Electric Operations Unaffiliated 1,573.6 1,672.6 1,564.2 Intersegment 0.8 0.8 0.7 Total 1,574.4 1,673.4 1,564.9 Corporate and Other Unaffiliated 9.5 6.2 7.7 Intersegment 396.4 412.5 370.2 Total 405.9 418.7 377.9 Eliminations (397.6 ) (413.6 ) (371.2 ) Consolidated Revenues $ 4,651.8 $ 5,272.4 $ 4,625.4 Year Ended December 31, (in millions) 2015 2014 2013 Operating Income (Loss) Gas Distribution Operations $ 555.8 $ 537.0 $ 445.4 Electric Operations 264.4 282.7 265.5 Corporate and Other (20.3 ) (30.6 ) (12.8 ) Consolidated $ 799.9 $ 789.1 $ 698.1 Depreciation and Amortization Gas Distribution Operations $ 232.6 $ 217.6 $ 201.4 Electric Operations 267.7 244.4 244.4 Corporate and Other 24.1 24.9 24.6 Consolidated $ 524.4 $ 486.9 $ 470.4 Assets Gas Distribution Operations $ 10,094.5 $ 9,443.7 Electric Operations 5,265.3 5,009.9 Corporate and Other (1) 2,132.7 10,136.2 Consolidated $ 17,492.5 $ 24,589.8 Capital Expenditures (2) Gas Distribution Operations $ 917.0 $ 860.3 $ 790.8 Electric Operations 400.3 438.8 426.3 Corporate and Other 50.2 40.5 31.4 Consolidated $ 1,367.5 $ 1,339.6 $ 1,248.5 (1) The 2014 balances for Corporate and Other includes assets of Discontinued Operations refer to Note 3 "Discontinued Operations," for additional information. (2) Amounts differ from those presented on the Statements of Consolidated Cash Flows primarily due to the inclusion of capital expenditures included in current liabilities and AFUDC Equity.

Quarterly Financial Data

Quarterly Financial Data	12 Months Ended
	Dec. 31, 2015
Quarterly Financial Data [Abstract]
Quarterly Financial Data	Quarterly Financial Data (Unaudited) Quarterly financial data does not always reveal the trend of NiSource’s business operations due to nonrecurring items and seasonal weather patterns, which affect earnings, and related components of net revenues and operating income. (in millions, except per share data) First Quarter Second Quarter Third Quarter Fourth Quarter 2015 Gross revenues $ 1,852.2 $ 884.6 $ 817.2 $ 1,097.8 Operating Income 386.3 84.4 109.7 219.5 Income (Loss) from Continuing Operations 192.5 (73.1 ) 14.8 64.4 Results from Discontinued Operations - net of taxes (1) 82.8 45.4 (19.7 ) (5.0 ) Net Income (Loss) 275.3 (27.7 ) (4.9 ) 59.4 Net Income (Loss) attributable to NiSource 268.4 (36.4 ) (4.9 ) 59.4 Basic Earnings (Loss) Per Share Continuing Operations 0.61 (0.23 ) 0.05 0.20 Discontinued Operations 0.24 0.12 (0.07 ) (0.01 ) Basic Earnings (Loss) Per Share $ 0.85 $ (0.11 ) $ (0.02 ) $ 0.19 Diluted Earnings (Loss) Per Share Continuing Operations 0.61 (0.23 ) 0.05 0.20 Discontinued Operations 0.24 0.12 (0.07 ) (0.01 ) Diluted Earnings (Loss) Per Share $ 0.85 $ (0.11 ) $ (0.02 ) $ 0.19 2014 Gross revenues $ 2,017.2 $ 1,023.7 $ 838.2 $ 1,393.3 Operating Income 373.3 117.8 71.1 226.9 Income (Loss) from Continuing Operations 173.1 20.8 (17.2 ) 79.5 Results from Discontinued Operations - net of taxes (1) 93.1 57.4 48.6 74.7 Net Income 266.2 78.2 31.4 154.2 Net Income attributable to NiSource 266.2 78.2 31.4 154.2 Basic Earnings Per Share Continuing Operations 0.55 0.07 (0.05 ) 0.25 Discontinued Operations 0.30 0.18 0.15 0.24 Basic Earnings Per Share $ 0.85 $ 0.25 $ 0.10 $ 0.49 Diluted Earnings Per Share Continuing Operations 0.55 0.07 (0.05 ) 0.25 Discontinued Operations 0.30 0.18 0.15 0.24 Diluted Earnings Per Share $ 0.85 $ 0.25 $ 0.10 $ 0.49 (1) Includes the results of the former Columbia Pipeline Group segment. On July 1, 2015, NiSource completed the Separation. The results of operations of the former Columbia Pipeline Group Operations segment have been classified as discontinued operations for all periods. As a result, certain quarterly financial data presented in the table above is different from the corresponding data originally filed on Form 10-Q or in Quarterly Financial Data (Unaudited) for those periods. The affected quarterly financial data originally filed for these periods is presented in the table below: (in millions) First Quarter Second Quarter Third Quarter Fourth Quarter 2015 Gross revenues $ 2,149.7 $ 1,169.0 Operating Income 530.1 165.1 Income (Loss) from Continuing Operations 275.3 (27.4 ) Results from Discontinued Operations - net of taxes $ — $ (0.3 ) 2014 Gross revenues $ 2,320.5 $ 1,335.1 $ 1,123.9 $ 1,691.1 Operating Income 533.7 219.6 157.8 351.3 Income from Continuing Operations 266.4 78.5 31.5 154.3 Results from Discontinued Operations - net of taxes $ (0.2 ) $ (0.3 ) $ (0.1 ) $ (0.1 )

Supplemental Cash Flow Informat

Supplemental Cash Flow Information	12 Months Ended
	Dec. 31, 2015
Supplemental Cash Flow Information [Abstract]
Supplemental Cash Flow Information	Supplemental Cash Flow Information The following tables provide additional information regarding NiSource’s Consolidated Statements of Cash Flows for the years ended December 31, 2015 , 2014 and 2013 : Year Ended December 31, (in millions) 2015 2014 2013 Supplemental Disclosures of Cash Flow Information Non-cash transactions: Capital expenditures included in current liabilities $ 121.6 $ 127.4 $ 96.7 Assets acquired under a capital lease 47.5 76.7 28.4 Schedule of interest and income taxes paid: Cash paid for interest, net of interest capitalized amounts $ 390.4 $ 429.3 $ 402.7 Cash paid for income taxes 21.3 19.4 10.4

Valuation And Qualifying Accoun

Valuation And Qualifying Accounts	12 Months Ended
	Dec. 31, 2015
Valuation and Qualifying Accounts [Abstract]
Schedule of Valuation and Qualifying Accounts Disclosure	N I S OURCE I NC . S CHEDULE II – V ALUATION AND Q UALIFYING ACCOUNTS Twelve months ended December 31, 2015 Additions ($ in millions) Balance Jan. 1, 2015 Charged to Costs and Expenses Charged to Other Account (1) Deductions for Purposes for which Reserves were Created Balance Dec. 31, 2015 Reserves Deducted in Consolidated Balance Sheet from Assets to Which They Apply: Reserve for accounts receivable $ 24.9 $ 22.5 $ 56.7 $ 83.8 $ 20.3 Reserve for other investments 3.0 — — — 3.0 Twelve months ended December 31, 2014 Additions ($ in millions) Balance Charged to Costs and Expenses Charged to Other Account (1) Deductions for Purposes for which Reserves were Created Balance Reserves Deducted in Consolidated Balance Sheet from Assets to Which They Apply: Reserve for accounts receivable $ 23.4 $ 21.8 $ 69.9 $ 90.2 $ 24.9 Reserve for other investments 3.0 — — — 3.0 Twelve months ended December 31, 2013 Additions ($ in millions) Balance Charged to Costs and Expenses Charged to Other Account (1) Deductions for Purposes for which Reserves were Created Balance Reserves Deducted in Consolidated Balance Sheet from Assets to Which They Apply: Reserve for accounts receivable $ 23.8 $ 13.8 $ 55.3 $ 69.5 $ 23.4 Reserve for other investments 3.0 — — — 3.0 (1) Charged to Other Accounts reflects the deferral of bad debt expense to a regulatory asset.

Nature Of Operations And Summ37

Nature Of Operations And Summary Of Significant Accounting Policies (Policy)	12 Months Ended
	Dec. 31, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Company Structure And Principles Of Consolidation	Company Structure and Principles of Consolidation . NiSource, a Delaware corporation, is an energy holding company whose subsidiaries are fully regulated natural gas and electric utility companies serving approximately 3.9 million customers in seven states. NiSource generates substantially all of its operating income through these rate-regulated businesses. The consolidated financial statements include the accounts of NiSource and its majority-owned subsidiaries after the elimination of all intercompany accounts and transactions. Investments for which at least a 20% interest is owned, certain joint ventures and limited partnership interests of more than 3% are accounted for under the equity method. Except where noted above and in the event where NiSource has significant influence, investments with less than a 20% interest are accounted for under the cost method. NiSource also consolidates variable interest entities for which NiSource is the primary beneficiary. On July 1, 2015, NiSource completed the Separation. CPG's operations consisted of all of NiSource's Columbia Pipeline Group Operations segment prior to the Separation. Following the Separation, NiSource retained no ownership interest in CPG. The results of operations and cash flows for the former Columbia Pipeline Group Operations segment have been reported as discontinued operations for all periods presented. Additionally, the assets and liabilities of the former Columbia Pipeline Group Operations segment were reclassified as assets and liabilities of discontinued operations for all prior periods. See Note 3, "Discontinued Operations," for additional information.
Use Of Estimates	Use of Estimates. The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements, and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates.
Cash, Cash Equivalents, And Restricted Cash	Cash, Cash Equivalents, and Restricted Cash . NiSource considers all investments with original maturities of three months or less to be cash equivalents. NiSource reports amounts deposited in brokerage accounts for margin requirements as restricted cash. In addition, NiSource has amounts deposited in trust to satisfy requirements for the provision of various property, liability, workers compensation, and long-term disability insurance, which is classified as restricted cash and disclosed as an investing cash flow on the Statements of Consolidated Cash Flows. Restricted cash was $ 29.7 million and $ 24.9 million as of December 31, 2015 and 2014 , respectively. The increase in restricted cash was primarily a result of higher margin requirements due to open derivative contracts.
Accounts Receivable And Unbilled Revenue	Accounts Receivable and Unbilled Revenue. Accounts receivable on the Consolidated Balance Sheets includes both billed and unbilled amounts as NiSource believes that total accounts receivable is a more meaningful presentation, given the factors which impact both billed and unbilled accounts receivable. Unbilled revenue is based on estimated amounts of electric energy or natural gas delivered but not yet billed to its customers. Unbilled amounts of accounts receivable relate to a portion of a customer’s consumption of gas or electricity from the date of the last cycle billing date through the last day of the month (balance sheet date). Factors taken into consideration when estimating unbilled revenue include historical usage, customer rates and weather. Accounts receivable fluctuates from year to year depending in large part on weather impacts and price volatility. NiSource’s accounts receivable on the Consolidated Balance Sheets includes unbilled revenue, less reserves, in the amounts of $237.1 million and $340.5 million for the years ended December 31, 2015 and 2014 , respectively. The reserve for uncollectible receivables is the Company’s best estimate of the amount of probable credit losses in the existing accounts receivable. The Company determined the reserve based on historical experience and in consideration of current market conditions. Account balances are charged against the allowance when it is anticipated the receivable will not be recovered.
Investments In Debt And Equity Securities	Investments in Debt and Equity Securities. NiSource’s investments in debt and equity securities are carried at fair value and are designated as available-for-sale. These investments are included within “Other investments” on the Consolidated Balance Sheets. Unrealized gains and losses, net of deferred income taxes, are reflected as accumulated other comprehensive income (loss). These investments are monitored for other than temporary declines in market value. Realized gains and losses and permanent impairments are reflected in the Statements of Consolidated Income. No material impairment charges were recorded for the years ended December 31, 2015 , 2014 and 2013 .
Basis Of Accounting For Rate-Regulated Subsidiaries	Basis of Accounting for Rate-Regulated Subsidiaries . Rate-regulated subsidiaries account for and report assets and liabilities consistent with the economic effect of the way in which regulators establish rates, if the rates established are designed to recover the costs of providing the regulated service and it is probable that such rates can be charged and collected. Certain expenses and credits subject to utility regulation or rate determination normally reflected in income are deferred on the Consolidated Balance Sheets and are recognized in income as the related amounts are included in customer rates and recovered from or refunded to customers. In the event that regulation significantly changes the opportunity for NiSource to recover its costs in the future, all or a portion of NiSource’s regulated operations may no longer meet the criteria for regulatory accounting. In such an event, a write-down of all or a portion of NiSource’s existing regulatory assets and liabilities could result. If transition cost recovery was approved by the appropriate regulatory bodies that would meet the requirements under GAAP for continued accounting as regulatory assets and liabilities during such recovery period, the regulatory assets and liabilities would be reported at the recoverable amounts. If unable to continue to apply the provisions of regulatory accounting, NiSource would be required to apply the provisions of ASC 980-20, Discontinuation of Rate-Regulated Accounting . In management’s opinion, NiSource’s regulated subsidiaries will be subject to regulatory accounting for the foreseeable future. Refer to Note 7, "Regulatory Matters," for additional information.
Utility Plant And Other Property And Related Depreciation And Maintenance	Utility Plant and Other Property and Related Depreciation and Maintenance . Property, plant and equipment (principally utility plant) is stated at cost. The rate-regulated subsidiaries record depreciation using composite rates on a straight-line basis over the remaining service lives of the electric, gas and common properties as approved by the appropriate regulators. The weighted average depreciation provisions for utility plant, as a percentage of the original cost, for the periods ended December 31, 2015 , 2014 and 2013 were as follows: 2015 2014 2013 Electric Operations 3.1 % 3.0 % 3.2 % Gas Distribution Operations 2.0 % 2.1 % 2.1 % For rate-regulated companies, AFUDC is capitalized on all classes of property except organization costs, land, autos, office equipment, tools and other general property purchases. The allowance is applied to construction costs for that period of time between the date of the expenditure and the date on which such project is placed in service. The pre-tax rate for AFUDC was 4.7% in 2015 , 4.5% in 2014 and 4.1% in 2013 . Generally, NiSource’s subsidiaries follow the practice of charging maintenance and repairs, including the cost of removal of minor items of property, to expense as incurred. When regulated property that represents a retired unit is replaced or removed, the cost of such property is credited to utility plant, and such cost, net of salvage, is charged to the accumulated provision for depreciation in accordance with composite depreciation.
Carrying Charges And Deferred Depreciation	Carrying Charges and Deferred Depreciation. NIPSCO has capitalized debt-based carrying charges and deferred depreciation related to Sugar Creek in accordance with the February 18, 2008 Order of the IURC. The deferral of Sugar Creek debt-based carrying charges and the deferral of depreciation ceased in December 2011 and deferred balances are being amortized over five years beginning January 2012. As of December 31, 2015 , the remaining balance to be amortized is $14.3 million . An additional $13.9 million is deferred for consideration in NIPSCO's current electric base rate case. Management believes this amount is probable of recovery through future rates. In 2005, the PUCO authorized Columbia of Ohio to revise its depreciation accrual rates for the period beginning January 1, 2005. The revised depreciation rates are now higher than those which would have been utilized if Columbia of Ohio were not subject to regulation. The amount of depreciation that would have been recorded for 2005 through 2015 had Columbia of Ohio not been subject to rate regulation is a combined $559.8 million , $66.4 million less than the $626.2 million reflected in rates. The regulatory asset was $65.3 million and $72.3 million as of December 31, 2015 and 2014 , respectively. The amount of depreciation that would have been recorded for 2015 had Columbia of Ohio not been subject to rate regulation is $74.7 million , $7.0 million less than the $81.7 million reflected in rates. Columbia of Ohio has PUCO approval to defer depreciation associated with its IRP and capital expenditure program. As of December 31, 2015, depreciation of $38.5 million was deferred for the programs. Recovery of the IRP depreciation is approved annually through the IRP rider (see Note 7, "Regulatory Matters"). The equivalent of annual depreciation expense, based on the average life of the related assets, is included in the calculation of the rider approved by the PUCO and billed to customers. Deferred depreciation expense is recognized as the rider is billed to customers. The recovery mechanism for depreciation associated with the capital expenditure program will be addressed in a separate proceeding.
Amortization Of Software Costs	Amortization of Software Costs. External and internal costs associated with computer software developed for internal use are capitalized. Capitalization of such costs commences upon the completion of the preliminary stage of each project. Once the installed software is ready for its intended use, such capitalized costs are amortized on a straight-line basis generally over a period of five years. NiSource amortized $41.1 million in 2015 , $33.7 million in 2014 and $31.3 million in 2013 related to software costs. NiSource’s unamortized software balance was $167.1 million and $162.3 million at December 31, 2015 and 2014 , respectively.
Goodwill And Other Intangible Assets	Goodwill and Other Intangible Assets. NiSource has $1,690.7 million in goodwill. Substantially all goodwill relates to the excess of cost over the fair value of the net assets acquired in the Columbia acquisition on November 1, 2000. In addition, NiSource has other intangible assets consisting primarily of franchise rights apart from goodwill that were identified as part of the purchase price allocations associated with the acquisition of Columbia of Massachusetts, a wholly-owned subsidiary of NiSource, which is being amortized on a straight-line basis over forty years from the date of acquisition. See Note 5, "Goodwill and Other Intangible Assets," for additional information.
Long-Lived Assets	K. Long-lived Assets. NiSource’s Consolidated Balance Sheets contain significant long-lived assets other than goodwill and intangible assets discussed above. As a result, NiSource assesses the carrying amount and potential earnings of these assets whenever events or changes in circumstances indicate that the carrying value could be impaired. There were no significant impairments for the years ended December 31, 2015, 2014 and 2013.
Revenue Recognition	Revenue Recognition. Revenue is recorded as products and services are delivered. Utility revenues are billed to customers monthly on a cycle basis. Revenues are recorded on the accrual basis and include estimates for electricity and gas delivered but not billed.
Earnings Per Share	Earnings Per Share. Basic EPS is computed by dividing net income attributable to NiSource by the weighted-average number of shares of common stock outstanding for the period. The weighted average shares outstanding for diluted EPS include the incremental effects of the various long-term incentive compensation plans. The numerator in calculating both basic and diluted EPS for each year is reported net income attributable to NiSource. The computation of diluted average common shares follows: Diluted Average Common Shares Computation 2015 2014 2013 Denominator (thousands) Basic average common shares outstanding 317,746 315,120 312,402 Dilutive potential common shares Nonqualified stock options — 6 80 Shares contingently issuable under employee stock plans (1) — 1,066 708 Shares restricted under stock plans (1) 2,090 444 456 Diluted Average Common Shares 319,836 316,636 313,646 (1) Change due to Separation-related adjustments, see Note 13, "Share-Based Compensation."
Estimated Rate Refunds	Estimated Rate Refunds . Certain rate-regulated subsidiaries collect revenues subject to refund pending final determination in rate proceedings. In connection with such revenues, estimated rate refund liabilities are recorded which reflect management’s current judgment of the ultimate outcomes of the proceedings. No provisions are made when, in the opinion of management, the facts and circumstances preclude a reasonable estimate of the outcome.
Accounts Receivable Transfer Program	Accounts Receivable Transfer Program. Certain of NiSource’s subsidiaries have agreements with third parties to sell certain accounts receivable without recourse. These transfers of accounts receivable are accounted for as secured borrowings. The entire gross receivables balance remains on the December 31, 2015 and 2014 Consolidated Balance Sheets and short-term debt is recorded in the amount of proceeds received from the purchasers involved in the transactions. Fees associated with the securitization transactions are recorded as interest expense. Refer to Note 17, "Transfers of Financial Assets," for further information.
Fuel Adjustment Clause	Fuel Adjustment Clause. NIPSCO defers most differences between fuel and power purchase costs and the recovery of such costs in revenue, and adjusts future billings for such deferrals on a basis consistent with applicable state-approved tariff provisions.
Gas Cost Adjustment Clause	Gas Cost Adjustment Clause. All of NiSource’s Gas Distribution Operations subsidiaries defer most differences between gas purchase costs and the recovery of such costs in revenues, and adjust future billings for such deferrals on a basis consistent with applicable state-approved tariff provisions.
Gas Inventory	Gas Inventory. Both the LIFO inventory methodology and the weighted average cost methodology are used to value natural gas in storage, as approved by regulators for each of NiSource’s regulated subsidiaries. Inventory valued using LIFO was $50.2 million and $55.1 million at December 31, 2015 , and 2014 , respectively. Based on the average cost of gas using the LIFO method, the estimated replacement cost of gas in storage was less than the stated LIFO cost by $27.2 million and $15.8 million at December 31, 2015 and 2014 , respectively. Inventory valued using the weighted average cost methodology was $293.3 million at December 31, 2015 and $385.2 million at December 31, 2014 .
Accounting For Exchange And Balancing Arrangements Of Natural Gas	Accounting for Exchange and Balancing Arrangements of Natural Gas. NiSource’s Gas Distribution Operations segment enters into balancing and exchange arrangements of natural gas as part of its operations and off-system sales programs. NiSource records a receivable or payable for its respective cumulative gas imbalances as well as for any gas inventory borrowed or lent under a Gas Distributions Operations exchange agreement. These receivables and payables are recorded as “Exchange gas receivable” or “Exchange gas payable” on NiSource’s Consolidated Balance Sheets, as appropriate.
Accounting For Risk Management Activities	Accounting for Risk Management Activities. NiSource accounts for its derivatives and hedging activities in accordance with ASC 815. NiSource recognizes all derivatives as either assets or liabilities on the Consolidated Balance Sheets at fair value, unless such contracts are exempted as a normal purchase normal sale under the provisions of the standard. The accounting for changes in the fair value of a derivative depends on the intended use of the derivative and resulting designation. There were no material derivative assets or liabilities as of December 31, 2015 and 2014.
Income Taxes And Investment Tax Credits	Income Taxes and Investment Tax Credits. NiSource records income taxes to recognize full interperiod tax allocations. Under the liability method, deferred income taxes are provided for the tax consequences of temporary differences by applying enacted statutory tax rates applicable to future years to differences between the financial statement carrying amount and the tax basis of existing assets and liabilities. Previously recorded investment tax credits of the regulated subsidiaries were deferred on the balance sheet and are being amortized to book income over the regulatory life of the related properties to conform to regulatory policy. To the extent certain deferred income taxes of the regulated companies are recoverable or payable through future rates, regulatory assets and liabilities have been established. Regulatory assets for income taxes are primarily attributable to property related tax timing differences for which deferred taxes had not been provided in the past, when regulators did not recognize such taxes as costs in the ratemaking process. Regulatory liabilities for income taxes are primarily attributable to the regulated companies’ obligation to refund to ratepayers deferred income taxes provided at rates higher than the current federal income tax rate. Such amounts are credited to ratepayers using either the average rate assumption method or the reverse South Georgia method. Pursuant to the U.S. Internal Revenue Code and relevant state taxing authorities, NiSource and its subsidiaries file consolidated income tax returns for federal and certain state jurisdictions. NiSource and its subsidiaries are parties to an agreement (the “Tax Allocation Agreement”) that provides for the allocation of consolidated tax liabilities. The Tax Allocation Agreement generally provides that each party is allocated an amount of tax similar to that which would be owed had the party been separately subject to tax. On June 30, 2015, in connection with the Separation, NiSource entered into an additional Tax Allocation Agreement with CPG to set forth their agreement with respect to tax matters for taxable periods prior to and including June 30, 2015.
Environmental Expenditures	Environmental Expenditures. NiSource accrues for costs associated with environmental remediation obligations when the incurrence of such costs is probable and the amounts can be reasonably estimated, regardless of when the expenditures are actually made. The undiscounted estimated future expenditures are based on currently enacted laws and regulations, existing technology and estimated site-specific costs where assumptions may be made about the nature and extent of site contamination, the extent of cleanup efforts, costs of alternative cleanup methods and other variables. The liability is adjusted as further information is discovered or circumstances change. The reserves for estimated environmental expenditures are recorded on the Consolidated Balance Sheets in “Legal and environmental” reserves for short-term portions of these liabilities and “Other noncurrent liabilities” for the respective long-term portions of these liabilities. Rate-regulated subsidiaries applying regulatory accounting establish regulatory assets on the Consolidated Balance Sheets to the extent that future recovery of environmental remediation costs is probable through the regulatory process. Refer to Note 18, "Other Commitments and Contingencies," for further information.
Excise Taxes	Excise Taxes. NiSource accounts for excise taxes that are customer liabilities by separately stating on its invoices the tax to its customers and recording amounts invoiced as liabilities payable to the applicable taxing jurisdiction. These types of taxes, comprised largely of sales taxes collected, are presented on a net basis affecting neither revenues nor cost of sales. NiSource accounts for taxes for which it is liable by recording a liability for the expected tax with a corresponding charge to “Other taxes” expense.

Nature Of Operations And Summ38

Nature Of Operations And Summary Of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Depreciation Provisions For Utility Plant As A Percentage Of The Original Cost	2015 2014 2013 Electric Operations 3.1 % 3.0 % 3.2 % Gas Distribution Operations 2.0 % 2.1 % 2.1 %
Computation Of Diluted Average Common Shares	Diluted Average Common Shares Computation 2015 2014 2013 Denominator (thousands) Basic average common shares outstanding 317,746 315,120 312,402 Dilutive potential common shares Nonqualified stock options — 6 80 Shares contingently issuable under employee stock plans (1) — 1,066 708 Shares restricted under stock plans (1) 2,090 444 456 Diluted Average Common Shares 319,836 316,636 313,646 (1) Change due to Separation-related adjustments, see Note 13, "Share-Based Compensation."

Discontinued Operations (Tables

Discontinued Operations (Tables)	12 Months Ended
	Dec. 31, 2015
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Disposal Groups, Including Discontinued Operations [Table Text Block]	Year Ended December 31, 2015 (in millions) Columbia Pipeline Group Operations Corporate and Other Total Net Revenues Transportation and storage revenues $ 561.4 $ — $ 561.4 Other revenues 94.3 — 94.3 Total Sales Revenues 655.7 — 655.7 Less: Cost of sales (excluding depreciation and amortization) 0.2 — 0.2 Net Revenues 655.5 — 655.5 Operating Expenses Operation and maintenance 375.8 (1) — 375.8 Depreciation and amortization 66.4 — 66.4 Gain on sale of assets (13.6 ) — (13.6 ) Other taxes 38.0 — 38.0 Total Operating Expenses 466.6 — 466.6 Equity Earnings in Unconsolidated Affiliates 29.1 — 29.1 Operating Income from Discontinued Operations 218.0 — 218.0 Other Income (Deductions) Interest expense, net (37.1 ) — (37.1 ) Other, net 7.8 0.4 8.2 Total Other Income (Deductions) (29.3 ) 0.4 (28.9 ) Income from Discontinued Operations before Income Taxes 188.7 0.4 189.1 Income Taxes 84.7 0.9 85.6 Income (Loss) from Discontinued Operations - net of taxes $ 104.0 $ (0.5 ) $ 103.5
Components of Net Income (Loss), Prior Year [Domain]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Disposal Groups, Including Discontinued Operations [Table Text Block]	Year Ended December 31, 2014 (in millions) Columbia Pipeline Group Operations Corporate and Other Total Net Revenues Transportation and storage revenues $ 1,034.3 $ — $ 1,034.3 Other revenues 312.9 — 312.9 Total Sales Revenues 1,347.2 — 1,347.2 Less: Cost of sales (excluding depreciation and amortization) 0.3 — 0.3 Net Revenues 1,346.9 — 1,346.9 Operating Expenses Operation and maintenance 769.1 (1) — 769.1 Depreciation and amortization 118.6 — 118.6 Gain on sale of assets (34.5 ) — (34.5 ) Other taxes 67.1 — 67.1 Total Operating Expenses 920.3 — 920.3 Equity Earnings in Unconsolidated Affiliates 46.6 — 46.6 Operating Income from Discontinued Operations 473.2 — 473.2 Other Income (Deductions) Interest expense, net (64.1 ) — (64.1 ) Other, net 8.9 (1.0 ) 7.9 Total Other Income (Deductions) (55.2 ) (1.0 ) (56.2 ) Income (Loss) from Discontinued Operations before Income Taxes 418.0 (1.0 ) 417.0 Income Taxes 143.5 (0.3 ) 143.2 Income (Loss) from Discontinued Operations - net of taxes $ 274.5 $ (0.7 ) $ 273.8
Components of Net Income Loss 2013 [Domain]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Disposal Groups, Including Discontinued Operations [Table Text Block]	Year Ended December 31, 2013 (in millions) Columbia Pipeline Group Operations Corporate and Other Total Net Revenues Transportation and storage revenues $ 971.1 $ — $ 971.1 Other revenues 208.7 2.5 211.2 Total Sales Revenues 1,179.8 2.5 1,182.3 Less: Cost of sales (excluding depreciation and amortization) 0.4 — 0.4 Net Revenues 1,179.4 2.5 1,181.9 Operating Expenses Operation and maintenance 619.5 — 619.5 Depreciation and amortization 106.9 — 106.9 Gain on sale of assets (18.6 ) — (18.6 ) Other taxes 62.2 — 62.2 Total Operating Expenses 770.0 — 770.0 Equity Earnings in Unconsolidated Affiliates 35.9 — 35.9 Operating Income from Discontinued Operations 445.3 2.5 447.8 Other Income (Deductions) Interest expense, net (39.5 ) — (39.5 ) Other, net 17.4 9.1 26.5 Total Other Income (Deductions) (22.1 ) 9.1 (13.0 ) Income from Discontinued Operations before Income Taxes 423.2 11.6 434.8 Income Taxes 153.3 5.3 158.6 Income from Discontinued Operations - net of taxes $ 269.9 $ 6.3 $ 276.2 Gain on Disposition of Discontinued Operations - net of taxes $ — $ 34.9 $ 34.9
Carrying Value of Assets [Domain]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Disposal Groups, Including Discontinued Operations [Table Text Block]	December 31, 2014 (in millions) Columbia Pipeline Group Operations Current Assets Cash and cash equivalents $ 0.5 Accounts receivable, net 149.3 Gas inventory 4.8 Materials and supplies, at average cost 24.9 Exchange gas receivable 34.8 Regulatory assets 6.1 Prepayments and other 63.0 Total current assets $ 283.4 Noncurrent Assets Net property, plant and equipment $ 4,959.7 Goodwill 1,975.5 Unconsolidated affiliates 444.3 Other investments 5.6 Regulatory assets 151.9 Deferred charges and other 9.0 Total noncurrent assets $ 7,546.0
Carrying Value of Liabilities [Domain]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Disposal Groups, Including Discontinued Operations [Table Text Block]	December 31, 2014 (in millions) Columbia Pipeline Group Operations Current Liabilities Accounts payable $ 60.5 Customer deposits and credits 13.4 Taxes accrued 106.9 Exchange gas payable 34.7 Deferred revenue 22.2 Regulatory liabilities 1.3 Accrued liability for postretirement and postemployment benefits 0.6 Legal and environmental 1.5 Accrued capital expenditures 61.1 Other accruals 66.8 Total current liabilities $ 369.0 Noncurrent Liabilities Deferred income taxes $ 1,214.3 Deferred investment tax credits 0.2 Deferred credits 0.2 Accrued liability for postretirement and postemployment benefits (1) (58.0 ) Regulatory liabilities 294.2 Asset retirement obligations 23.2 Other noncurrent liabilities 84.3 Total noncurrent liabilities $ 1,558.4

Property, Plant And Equipment (

Property, Plant And Equipment (Tables)	12 Months Ended
	Dec. 31, 2015
Property, Plant and Equipment [Abstract]
Schedule Of Property, Plant And Equipment	At December 31, (in millions) 2015 2014 Property Plant and Equipment Gas Distribution Utility (1) $ 10,620.4 $ 9,753.9 Electric Utility (1) 7,765.7 7,160.0 Common Utility 107.2 181.5 Construction Work in Process 453.6 573.0 Non-Utility and Other 41.2 43.1 Total Property, Plant and Equipment $ 18,988.1 $ 17,711.5 Accumulated Depreciation and Amortization Gas Distribution Utility (1) $ (3,029.0 ) $ (2,922.7 ) Electric Utility (1) (3,767.7 ) (3,596.5 ) Common Utility (56.7 ) (110.3 ) Non-Utility and Other (23.2 ) (24.6 ) Total Accumulated Depreciation and Amortization $ (6,876.6 ) $ (6,654.1 ) Net Property, Plant and Equipment $ 12,111.5 $ 11,057.4 (1) NIPSCO’s common utility plant and associated accumulated depreciation and amortization are allocated between Gas Distribution Utility and Electric Utility Property, Plant and Equipment.

Goodwill and Other Intangible41

Goodwill and Other Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2015
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Goodwill [Table Text Block]	(in millions) Gas Distribution Operations Electric Operations Corporate and Other Total Goodwill $ 1,690.7 $ — $ — $ 1,690.7

Asset Retirement Obligations (T

Asset Retirement Obligations (Tables)	12 Months Ended
	Dec. 31, 2015
Asset Retirement Obligation [Abstract]
Changes In Liability For Asset Retirement Obligations	(in millions) 2015 2014 Beginning Balance $ 136.2 $ 148.1 Accretion recorded as a regulatory asset/liability 8.6 8.2 Additions 6.5 0.3 Settlements (7.0 ) (2.2 ) Change in estimated cash flows (1) 109.7 (18.2 ) Ending Balance $ 254.0 $ 136.2 (1) The change in estimated cash flows for 2015 is primarily attributable to estimated costs associated with the EPA's final rule for regulation of CCRs and changes to cost estimates for certain solid waste management units. See Note 18, "Other Commitments and Contingencies," for additional information on CCRs. The change in estimated cash flows for 2014 is primarily attributed to changes in estimated costs and settlement timing for electric generating stations and to retire pipeline.

Regulatory Matters (Tables)

Regulatory Matters (Tables)	12 Months Ended
	Dec. 31, 2015
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory Assets	At December 31, (in millions) 2015 2014 Assets Unrecognized pension benefit and other postretirement benefit costs (see Note 10) $ 928.7 $ 910.3 Other postretirement costs 47.0 46.7 Environmental costs (see Note 18-C) 62.2 65.9 Regulatory effects of accounting for income taxes (see Note 1-U) 234.1 231.8 Underrecovered gas costs (see Note 1-P and 1-Q) 34.8 32.0 Depreciation (see Note 1-H) 124.5 116.4 Uncollectible accounts receivable deferred for future recovery 17.0 26.1 Post-in-service carrying charges 107.2 87.8 EERM operation and maintenance and depreciation deferral 48.1 31.1 Sugar Creek carrying charges and deferred depreciation (see Note 1-H) 28.2 42.5 DSM Program 35.6 37.9 Other 139.3 135.4 Total Assets $ 1,806.7 $ 1,763.9 Less amounts included as Underrecovered gas cost (34.8 ) (32.0 ) Total Regulatory Assets reflected in Current Regulatory Assets and Other Regulatory Assets $ 1,771.9 $ 1,731.9
Regulatory Liabilities	At December 31, (in millions) 2015 2014 Liabilities Overrecovered gas and fuel costs (see Notes 1-P and 1-Q) $ 148.1 $ 45.6 Cost of removal (see Note 6) 1,261.5 1,287.0 Regulatory effects of accounting for income taxes (see Note 1-U) 34.2 42.3 Unrecognized pension benefit and other postretirement benefit costs (see Note 10) 8.1 10.1 Other postretirement costs 38.8 31.9 Other 91.1 69.4 Total Liabilities $ 1,581.8 $ 1,486.3 Less amounts included as Overrecovered gas and fuel cost (148.1 ) (45.6 ) Total Regulatory Liabilities reflected in Current Regulatory Liabilities and Other Regulatory Liabilities and Other Removal Costs $ 1,433.7 $ 1,440.7

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Schedule Of Components Of Income Tax Expense	Year Ended December 31, (in millions) 2015 2014 2013 Income Taxes Current Federal $ — $ — $ (11.6 ) State 6.0 5.4 1.8 Total Current 6.0 5.4 (9.8 ) Deferred Federal 124.1 129.5 125.6 State 13.6 35.4 (3.4 ) Total Deferred 137.7 164.9 122.2 Deferred Investment Credits (2.4 ) (3.5 ) (3.8 ) Income Taxes from Continuing Operations $ 141.3 $ 166.8 $ 108.6
Schedule Of Reasons Behind Differences In Computation Of Total Income Taxes	Year Ended December 31, (in millions) 2015 2014 2013 Book income from Continuing Operations before income taxes $ 339.9 $ 423.0 $ 329.6 Tax expense at statutory federal income tax rate 118.9 35.0 % 148.1 35.0 % 115.4 35.0 % Increases (reductions) in taxes resulting from: State income taxes, net of federal income tax benefit 14.8 4.4 15.7 3.7 2.3 0.7 Regulatory treatment of depreciation differences 4.3 1.3 0.7 0.2 (0.5 ) (0.2 ) Amortization of deferred investment tax credits (2.4 ) (0.7 ) (3.5 ) (0.8 ) (3.8 ) (1.2 ) Nondeductible expenses 2.1 0.6 0.8 0.2 2.4 0.7 Employee stock ownership plan dividends (2.9 ) (0.9 ) (3.8 ) (0.9 ) (3.6 ) (1.0 ) AFUDC equity (3.5 ) (1.0 ) (3.5 ) (0.8 ) (3.4 ) (1.0 ) Charitable contribution carryover 17.8 5.2 — — — — Tax accrual adjustments and other, net (7.8 ) (2.3 ) 12.3 2.8 (0.2 ) (0.1 ) Income Taxes from Continuing Operations $ 141.3 41.6 % $ 166.8 39.4 % $ 108.6 32.9 %
Schedule Of Principal Components Of Net Deferred Tax Liability	At December 31, (in millions) 2015 2014 Deferred tax liabilities Accelerated depreciation and other property differences $ 3,510.8 $ 2,964.6 Unrecovered gas and fuel costs 11.2 11.4 Other regulatory assets 403.3 610.6 Premiums and discounts associated with long-term debt 9.9 12.5 Total Deferred Tax Liabilities 3,935.2 3,599.1 Deferred tax assets Other regulatory liabilities (74.4 ) (79.3 ) Cost of removal (519.4 ) (527.7 ) Pension and other postretirement/postemployment benefits (243.8 ) (191.9 ) Environmental liabilities (45.9 ) (52.1 ) Net operating loss carryforward and Alternative Minimum Tax credit carryforward (437.4 ) (372.7 ) Other accrued liabilities (89.0 ) (58.9 ) Other, net (160.0 ) (150.7 ) Total Deferred Tax Assets (1,569.9 ) (1,433.3 ) Net Deferred Tax Liabilities $ 2,365.3 $ 2,165.8
Schedule Of Reconciliation Of The Beginning And Ending Amounts Of Unrecognized Tax Benefits	Reconciliation of Unrecognized Tax Benefits (in millions) 2015 2014 2013 Unrecognized Tax Benefits - Opening Balance $ 24.4 $ 23.7 $ 28.4 Gross increases - tax positions in prior period 0.4 — 1.6 Gross decreases - tax positions in prior period (23.9 ) (1.0 ) (21.4 ) Gross increases - current period tax positions — 1.7 15.1 Unrecognized Tax Benefits - Ending Balance $ 0.9 $ 24.4 $ 23.7 Offset for net operating loss carryforwards (0.9 ) (24.2 ) (23.0 ) Balance - Net of Net Operating Loss Carryforwards $ — $ 0.2 $ 0.7

Pension And Other Postretirem45

Pension And Other Postretirement Benefits (Tables)	12 Months Ended
	Dec. 31, 2015
Pension and Other Postretirement Benefit Expense [Abstract]
Schedule Of Allocation of Plan Assets	Defined Benefit Pension Plan Postretirement Benefit Plan Asset Category Minimum Maximum Minimum Maximum Domestic Equities 25% 45% 35% 55% International Equities 15% 25% 15% 25% Fixed Income 23% 37% 20% 50% Real Estate/Private Equity/Hedge Funds 0% 15% 0% 0% Short-Term Investments 0% 10% 0% 10% Pension Plan and Postretirement Plan Asset Mix at December 31, 2015 and December 31, 2014 : (in millions) Defined Benefit Pension Assets December 31, Postretirement December 31, Asset Class Asset Value % of Total Assets Asset Value % of Total Assets Domestic Equities $ 686.3 39.3 % $ 105.0 46.5 % International Equities 323.2 18.5 % 39.6 17.5 % Fixed Income 619.3 35.5 % 79.1 35.0 % Real Estate/Private Equity/Hedge Funds 96.7 5.5 % — — Cash/Other 21.6 1.2 % 2.2 1.0 % Total $ 1,747.1 100.0 % $ 225.9 100.0 % (in millions) Defined Benefit Pension Assets December 31, Postretirement Benefit Plan Assets December 31, Asset Class Asset Value % of Total Assets Asset Value % of Total Assets Domestic Equities $ 957.2 41.1 % $ 219.6 47.2 % International Equities 420.5 18.1 % 85.6 18.4 % Fixed Income 802.4 34.4 % 158.6 34.1 % Real Estate/Private Equity/Hedge Funds 117.6 5.0 % — — Cash/Other 32.6 1.4 % 1.2 0.3 % Total $ 2,330.3 100.0 % $ 465.0 100.0 %
Schedule Of Fair Value and Changes In The Fair Value Of The Plan Assets	Fair Value Measurements at December 31, 2015 : (in millions) December 31, Quoted Prices in Active Significant Other Significant Pension plan assets: Cash $ 7.0 $ 7.0 $ — $ — Equity securities International equities 45.3 45.3 — — Fixed income securities Government 64.6 — 64.6 — Corporate 95.8 — 95.8 — Other fixed income 0.1 — — 0.1 Mutual Funds U.S. multi-strategy 257.1 257.1 — — International equities 64.9 64.9 — — Fixed income 150.5 150.5 — — Private equity limited partnerships U.S. multi-strategy (1) 46.4 — — 46.4 International multi-strategy (2) 29.3 — — 29.3 Distressed opportunities 5.9 — — 5.9 Real estate 13.6 — — 13.6 Commingled funds Short-term money markets (3) 22.9 U.S. equities (3) 429.2 International equities (3) 210.1 Fixed income (3) 302.5 Pension plan assets subtotal 1,745.2 524.8 160.4 95.3 Other postretirement benefit plan assets: Mutual funds U.S. equities 89.8 89.8 — — International equities 41.4 41.4 — — Fixed income 78.0 78.0 — — Commingled funds Short-term money markets (3) 2.4 U.S. equities (3) 14.3 Other postretirement benefit plan assets subtotal 225.9 209.2 — — Due to brokers, net (4) (0.2 ) Receivables/payables 2.1 Total pension and other post-retirement benefit plan assets $ 1,973.0 $ 734.0 $ 160.4 $ 95.3 (1) This class includes limited partnerships/fund of funds that invest in a diverse portfolio of private equity strategies, including buy-outs, venture capital, growth capital, special situations and secondary markets, primarily inside the United States. (2) This class includes limited partnerships/fund of funds that invest in diverse portfolio of private equity strategies, including buy-outs, venture capital, growth capital, special situations and secondary markets, primarily outside the United States. (3) This class of investments is measured at fair value using the net asset value per share and has not been classified in the fair value hierarchy. (4) This class represents pending trades with brokers. The table below sets forth a summary of changes in the fair value of the Plan’s Level 3 assets for the year ended December 31, 2015 : Balance at January 1, 2015 Total gains or losses (unrealized / realized) Purchases (Sales) Transfers into/(out of) level 3 Balance at December 31, 2015 Fixed income securities Other fixed income $ 0.6 $ — $ — $ (0.5 ) $ — $ 0.1 Private equity limited partnerships U.S. multi-strategy 56.2 (3.5 ) 1.1 (7.4 ) — 46.4 International multi-strategy 35.3 (2.3 ) 0.1 (3.8 ) — 29.3 Distressed opportunities 7.6 (0.5 ) — (1.2 ) — 5.9 Real estate 17.3 (0.5 ) 0.1 (3.3 ) — 13.6 Total $ 117.0 $ (6.8 ) $ 1.3 $ (16.2 ) $ — $ 95.3 The table below sets forth a summary of unfunded commitments, redemption frequency and redemption notice periods for certain investments that are measured at fair value using the net asset value per share for the year ended December 31, 2015 : (in millions) Fair Value Unfunded Commitments Redemption Frequency Redemption Notice Period Commingled Funds Short-term money markets $ 25.3 $ — Daily 1 day U.S. equities 443.5 — Monthly 3 days International equities 210.1 — Monthly 14-30 days Fixed income 302.5 — Monthly 3 days Total $ 981.4 $ — Fair Value Measurements at December 31, 2014 : (in millions) December 31, Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Significant Pension plan assets: Cash $ 17.1 $ 17.1 $ — $ — Equity securities U.S. equities 0.4 0.4 — — International equities 134.5 133.9 0.6 — Fixed income securities Government 118.4 104.6 13.8 — Corporate 257.0 — 257.0 — Mortgages/Asset backed securities 2.7 — 2.7 — Other fixed income 0.6 — — 0.6 Private equity limited partnerships U.S. multi-strategy (1) 56.2 — — 56.2 International multi-strategy (2) 35.3 — — 35.3 Distressed opportunities 7.6 — — 7.6 Real Estate 17.3 — — 17.3 Commingled funds Short-term money markets (3) 32.6 U.S. equities (3) 957.2 International equities (3) 279.9 Fixed income (3) 409.0 Pension plan assets subtotal 2,325.8 256.0 274.1 117.0 Other postretirement benefit plan assets: Mutual funds U.S. equities 189.8 189.8 — — International equities 85.6 85.6 — — Fixed income 158.2 158.2 — — Commingled funds Short-term money markets (3) 1.6 U.S. equities (3) 29.8 Other postretirement benefit plan assets subtotal 465.0 433.6 — — Due to brokers, net (4) (0.6 ) Accrued investment income/dividends 4.6 Receivables/payables 0.5 Total pension and other post-retirement benefit plan assets $ 2,795.3 $ 689.6 $ 274.1 $ 117.0 (1) This class includes limited partnerships/fund of funds that invest in a diverse portfolio of private equity strategies, including buy-outs, venture capital, growth capital, special situations and secondary markets, primarily in the United States. (2) This class includes limited partnerships/fund of funds that invest in a diverse portfolio of private equity strategies, including buy-outs, venture capital, growth capital, special situations and secondary markets, primarily outside the United States. (3) This class of investments is measured at fair value using the net asset value per share and has not been classified in the fair value hierarchy. (4) This class represents pending trades with brokers. The table below sets forth a summary of changes in the fair value of the Plan’s Level 3 assets for the year ended December 31, 2014 : Balance at January 1, 2014 Total gains or losses (unrealized / realized) Purchases (Sales) Transfers into/(out of) level 3 Balance at December 31, 2014 Fixed income securities Mortgages/Asset backed securities $ 0.1 $ — $ — $ (0.1 ) $ — $ — Other fixed income — 0.3 0.3 — — 0.6 Private equity limited partnerships U.S. multi-strategy 57.9 2.7 2.5 (6.9 ) — 56.2 International multi-strategy 38.2 (0.4 ) 0.5 (3.0 ) — 35.3 Distress opportunities 8.9 0.5 0.1 (1.9 ) — 7.6 Real estate 19.6 2.3 0.1 (4.7 ) — 17.3 Total $ 124.7 $ 5.4 $ 3.5 $ (16.6 ) $ — $ 117.0 The table below sets forth a summary of unfunded commitments, redemption frequency and redemption notice periods for certain investments that are measured at fair value using the net asset value per share for the year ended December 31, 2014 : (in millions) Fair Value Unfunded Commitments Redemption Frequency Redemption Notice Period Commingled Funds Short-term money markets $ 34.2 $ — Daily 1 day U.S. equities 987.0 — Monthly 3 days International equities 279.9 — Monthly 14-30 days Fixed income 409.0 — Monthly 3 days Total $ 1,710.1 $ —
Schedule Of Reconciliation Of The Plan Funded Status	Pension Benefits Other Postretirement Benefits (in millions) 2015 2014 2015 2014 Change in projected benefit obligation (1) Benefit obligation at beginning of year $ 2,751.4 $ 2,528.2 $ 716.0 $ 714.2 Service cost 34.8 34.8 6.4 8.5 Interest cost 95.9 109.0 24.9 30.1 Plan participants’ contributions — — 7.3 9.1 Plan amendments — 0.6 0.1 (41.5 ) Actuarial loss (gain) (91.7 ) 272.1 (71.5 ) 47.6 Settlement loss 0.5 — — — Benefits paid (171.8 ) (193.3 ) (43.7 ) (53.7 ) Estimated benefits paid by incurred subsidy — — 0.8 1.7 Separation of CPG (Note 3) (412.4 ) — (114.5 ) — Projected benefit obligation at end of year $ 2,206.7 $ 2,751.4 $ 525.8 $ 716.0 Change in plan assets Fair value of plan assets at beginning of year $ 2,330.3 $ 2,267.3 $ 465.0 $ 454.2 Actual return on plan assets (49.7 ) 200.4 1.9 20.3 Employer contributions 2.7 55.9 25.8 35.1 Plan participants’ contributions — — 7.3 9.1 Benefits paid (171.8 ) (193.3 ) (43.7 ) (53.7 ) Separation of CPG (Note 3) (364.4 ) — (230.4 ) — Fair value of plan assets at end of year $ 1,747.1 $ 2,330.3 $ 225.9 $ 465.0 Funded Status at end of year $ (459.6 ) $ (421.1 ) $ (299.9 ) $ (251.0 ) Amounts recognized in the statement of financial position consist of: Current liabilities (3.0 ) (3.5 ) (0.6 ) (0.6 ) Noncurrent liabilities (456.6 ) (417.6 ) (299.3 ) (250.4 ) Net amount recognized at end of year (2) $ (459.6 ) $ (421.1 ) $ (299.9 ) $ (251.0 ) Amounts recognized in accumulated other comprehensive income or regulatory asset/liability (3) Unrecognized prior service credit $ 0.7 $ (3.5 ) $ (41.6 ) $ (49.2 ) Unrecognized actuarial loss 925.6 1,009.8 66.1 95.5 $ 926.3 $ 1,006.3 $ 24.5 $ 46.3 (1) The change in benefit obligation for Pension Benefits represents the change in Projected Benefit Obligation while the change in benefit obligation for Other Postretirement Benefits represents the change in Accumulated Postretirement Benefit Obligation. (2) NiSource recognizes in its Consolidated Balance Sheets the underfunded and overfunded status of its various defined benefit postretirement plans, measured as the difference between the fair value of the plan assets and the benefit obligation. (3) NiSource determined that for certain rate-regulated subsidiaries the future recovery of pension and other postretirement benefits costs is probable. These rate-regulated subsidiaries recorded regulatory assets and liabilities of $928.7 million and $8.1 million , respectively, as of December 31, 2015 , and $910.3 million and $10.1 million , respectively, as of December 31, 2014 that would otherwise have been recorded to accumulated other comprehensive loss.
Schedule Of Significant Actuarial Assumptions In Determining Funded Status Plan	Pension Benefits Other Postretirement Benefits 2015 2014 2015 2014 Weighted-average assumptions to Determine Benefit Obligation Discount Rate 4.24 % 3.81 % 4.33 % 3.94 % Rate of Compensation Increases 4.00 % 4.00 % — — Health Care Trend Rates Trend for Next Year — — 8.41 % 6.90 % Ultimate Trend — — 4.50 % 4.50 % Year Ultimate Trend Reached — — 2022 2021
Schedule Of One-Percentage-Point Change In Assumed Health Care Cost Trend Rates	(in millions) 1% point increase 1% point decrease Effect on service and interest components of net periodic cost $ 1.7 $ (1.5 ) Effect on accumulated postretirement benefit obligation 32.4 (28.0 )
Schedule Of Expected Payments To Participants In Pension Plan	(in millions) Pension Benefits Other Federal Year(s) 2016 $ 174.1 $ 34.7 $ 0.9 2017 175.8 35.4 0.9 2018 177.1 36.0 0.9 2019 176.1 36.7 0.9 2020 174.5 37.0 0.9 2021-2025 837.8 181.5 3.6
Components Of The Plans' Net Periodic Benefits Cost	Pension Benefits Other Postretirement Benefits (in millions) 2015 2014 2013 2015 2014 2013 Components of Net Periodic Benefit Cost (Income) Service cost $ 34.8 $ 34.8 $ 36.4 $ 6.4 $ 8.5 $ 12.1 Interest cost 95.9 109.0 98.9 24.9 30.1 32.2 Expected return on assets (167.2 ) (181.1 ) (168.1 ) (28.2 ) (36.8 ) (30.3 ) Amortization of transitional obligation — — — — — 0.5 Amortization of prior service cost (credit) 0.1 0.2 0.3 (5.2 ) (4.3 ) (0.7 ) Recognized actuarial loss 59.3 47.5 77.8 3.4 0.4 11.0 Net Periodic Benefit Costs (Income) 22.9 10.4 45.3 1.3 (2.1 ) 24.8 Additional loss recognized due to: Settlement loss 2.5 — 33.4 — — — Total Net Periodic Benefits Cost (Income) $ 25.4 $ 10.4 $ 78.7 $ 1.3 $ (2.1 ) $ 24.8
Schedule Of Key Assumptions That Were Used To Calculate The Net Periodic Benefits Cost	Pension Benefits Other Postretirement Benefits 2015 2014 2013 2015 2014 2013 Weighted-average Assumptions to Determine Net Periodic Benefit Cost Discount Rate 3.81 % 4.50 % 3.63 % 3.94 % 4.75 % 3.95 % Expected Long-Term Rate of Return on Plan Assets 8.30 % 8.30 % 8.30 % 8.15 % 8.14 % 8.14 % Rate of Compensation Increases 4.00 % 4.00 % 4.00 % — — —
Schedule Of Changes In Plan Assets And Projected Benefit Obligations Recognized In Other Comprehensive Income	Pension Benefits Other Postretirement Benefits (in millions) 2015 2014 2015 2014 Other Changes in Plan Assets and Projected Benefit Obligations Recognized in Other Comprehensive Income or Regulatory Asset or Liability Net prior service cost (credit) $ — $ 0.6 $ 0.1 $ (41.5 ) Net actuarial loss (gain) 125.7 252.8 (45.2 ) 64.0 Settlements (2.5 ) — — — Less: amortization of prior service cost (credit) (0.1 ) (0.2 ) 5.2 4.3 Less: amortization of net actuarial loss (gain) (59.3 ) (47.5 ) (3.4 ) (0.4 ) Less: Separation of CPG (Note 3) (143.8 ) — 21.5 — Total Recognized in Other Comprehensive Income or Regulatory Asset or Liability $ (80.0 ) $ 205.7 $ (21.8 ) $ 26.4 Amount Recognized in Net Periodic Benefits Cost and Other Comprehensive Income or Regulatory Asset or Liability $ (54.6 ) $ 216.1 $ (20.5 ) $ 24.3

Share-Based Compensation (Table

Share-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2015
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Schedule Of Transactions Of Share Based Compensation Other Than Stock Options	Restricted Stock Units Weighted Average Grant Date Fair Value ($) (1) Nonvested at December 31, 2014 307,329 27.92 Granted 660,230 36.23 Forfeited (22,860 ) 16.98 Vested (94,380 ) 20.61 Awards surrendered as a result of the Separation (445,123 ) Awards granted in conversion as a result of the Separation 547,148 Nonvested and Expected to Vest 952,344 14.38 Performance Shares Converted to Restricted Stock Units as a result of the Separation 2,190,129 6.01 Nonvested and Expected to Vest at December 31, 2015 3,142,473 8.55 (1) The reduction in weighted average grant date fair value during 2015 primarily resulted from the significant number of incremental units issued as a result of the Separation. As discussed above in "Separation-related Adjustments," these incremental units were issued to preserve the intrinsic value of such awards immediately before the Separation.	[1]
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Schedule Of Transactions Of Share Based Compensation Other Than Stock Options	Performance Awards Weighted Average Grant Date Fair Value ($) Nonvested at December 31, 2014 1,727,855 24.80 Granted — — Forfeited (110,013 ) 9.24 Vested (649,896 ) 20.29 Awards surrendered as a result of the Separation (573,486 ) Awards granted in conversion as a result of the Separation 1,795,669 Performance Shares at July 1, 2015 2,190,129 6.01 Awards Converted to Restricted Stock Units as a result of the Separation (2,190,129 ) Nonvested and Expected to Vest at December 31, 2015 — —
[1]	The reduction in weighted average grant date fair value during 2015 primarily resulted from the significant number of incremental units issued as a result of the Separation. As discussed above in "Separation-related Adjustments," these incremental units were issued to preserve the intrinsic value of such awards immediately before the Separation.

Long-Term Debt (Tables)

Long-Term Debt (Tables)	12 Months Ended
	Dec. 31, 2015
Long-term Debt, Current and Noncurrent [Abstract]
Schedule Of Outstanding Long Term Debt Sinking Fund Requirements And Maturities	Year Ending December 31, (in millions) 2016 $ 433.7 2017 362.2 2018 488.9 2019 554.7 2020 563.8 After 4,024.4 Total (1) $ 6,427.7 (1) This amount excludes $45.5 million of unamortized discount, premium and expenses.

Short-Term Borrowings (Tables)

Short-Term Borrowings (Tables)	12 Months Ended
	Dec. 31, 2015
Short-term Debt [Abstract]
Schedule Of Short-Term Borrowings	At December 31, (in millions) 2015 2014 Commercial Paper weighted average interest rate of 1.00 % and 0.82% at December 31, 2015 and 2014, respectively. $ 321.4 $ 792.6 Credit facilities borrowings weighted average interest rate of 1.44% at December 31, 2014. — 500.0 Accounts receivable securitization facility borrowings 246.0 284.3 Total Short-Term Borrowings $ 567.4 $ 1,576.9

Fair Value (Tables)

Fair Value (Tables)	12 Months Ended
	Dec. 31, 2015
Fair Value Disclosures [Abstract]
Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis	Recurring Fair Value Measurements December 31, 2015 ( in millions ) Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Balance as of December 31, 2015 Assets Price risk management assets: Commodity financial price risk programs $ 0.1 $ — $ — $ 0.1 Available-for-sale securities — 128.7 — 128.7 Total $ 0.1 $ 128.7 $ — $ 128.8 Liabilities Price risk management liabilities: Commodity financial price risk programs $ 14.3 $ — $ 0.2 $ 14.5 Interest rate risk activities — 17.4 — 17.4 Total $ 14.3 $ 17.4 $ 0.2 $ 31.9 Recurring Fair Value Measurements December 31, 2014 ( in millions ) Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Balance as of December 31, 2014 Assets Price risk management assets: Commodity financial price risk programs 0.1 — — 0.1 Available-for-sale securities 28.4 103.5 — 131.9 Total $ 28.5 $ 103.5 $ — $ 132.0 Liabilities Price risk management liabilities: Commodity financial price risk programs $ 14.2 $ — $ 0.1 $ 14.3 Total $ 14.2 $ — $ 0.1 $ 14.3
Available-For-Sale Debt Securities	December 31, 2015 (in millions) Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Available-for-sale debt securities U.S. Treasury securities $ 33.7 $ 0.1 $ (0.3 ) $ 33.5 Corporate/Other bonds 95.7 0.3 (0.8 ) 95.2 Total $ 129.4 $ 0.4 $ (1.1 ) $ 128.7 December 31, 2014 (in millions) Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Available-for-sale debt securities U.S. Treasury securities $ 30.8 $ 0.3 $ (0.2 ) $ 30.9 Corporate/Other bonds 100.6 1.0 (0.6 ) 101.0 Total $ 131.4 $ 1.3 $ (0.8 ) $ 131.9
Carrying Amount And Estimated Fair Values Of Financial Instruments	At December 31, (in millions) Carrying Amount 2015 Estimated Fair Value 2015 Carrying Amount 2014 Estimated Fair Value 2014 Long-term debt (including current portion) $ 6,382.2 $ 6,975.7 $ 8,418.1 $ 9,505.7

Transfers Of Financial Assets (

Transfers Of Financial Assets (Tables)	12 Months Ended
	Dec. 31, 2015
Transfers and Servicing [Abstract]
Schedule of Assets and Associated Liabilities Accounted for as Secured Borrowings	(in millions) December 31, December 31, Gross Receivables $ 450.8 $ 611.7 Less: Receivables not transferred 204.8 327.4 Net receivables transferred $ 246.0 $ 284.3 Short-term debt due to asset securitization $ 246.0 $ 284.3

Other Commitments And Conting51

Other Commitments And Contingencies (Tables)	12 Months Ended
	Dec. 31, 2015
Commitments and Contingencies Disclosure [Abstract]
Future Minimum Lease Payments Required Under Operating And Capital Leases	(in millions) Operating Leases (1) Capital Leases (2) 2016 $ 18.4 $ 23.5 2017 11.1 23.0 2018 8.8 23.3 2019 7.0 23.7 2020 3.5 23.5 After 13.3 196.3 Total future minimum payments $ 62.1 $ 313.3 (1) Operating lease balances do not include amounts for fleet leases that can be renewed beyond the initial lease term. The Company anticipates renewing the leases beyond the initial term, but the anticipated payments associated with the renewals do not meet the definition of expected minimum lease payments and therefore are not included above. Expected payments are $30.5 million in 2016, $30.9 million in 2017, $26.7 million in 2018, $20.3 million in 2019, $12.5 million in 2020 and $7.5 million thereafter. (2) Capital lease payments shown above are inclusive of interest totaling $114.7 million .
Estimated Aggregate Amounts Of Minimum Fixed Payments On Purchase And Service Obligations	(in millions) Energy Commodity Agreements Pipeline Service Agreements IBM Service Agreement Other Service Agreements Total 2016 $ 169.3 $ 512.7 $ 90.9 $ 72.0 $ 844.9 2017 74.8 496.0 82.8 67.2 720.8 2018 67.5 341.0 80.1 19.7 508.3 2019 70.6 245.4 78.6 4.6 399.2 2020 72.6 139.3 77.7 2.3 291.9 After 0.4 429.9 — — 430.3 Total purchase and service obligations $ 455.2 $ 2,164.3 $ 410.1 $ 165.8 $ 3,195.4

Accumulated Other Comprehensi52

Accumulated Other Comprehensive Loss (Tables)	12 Months Ended
	Dec. 31, 2015
Components of Accumulated Other Comprehensive Income (Loss) [Abstract]
Schedule of Accumulated Other Comprehensive Income (Loss)	(in millions) Gains and Losses on Securities (1) Gains and Losses on Cash Flow Hedges (1) Pension and OPEB Items (1) Accumulated Other Comprehensive Loss (1) Balance as of January 1, 2013 $ 2.6 $ (28.6 ) $ (39.5 ) $ (65.5 ) Other comprehensive income before reclassifications (2.4 ) 0.1 17.8 15.5 Amounts reclassified from accumulated other comprehensive income (0.5 ) 2.7 4.2 6.4 Net current-period other comprehensive income (loss) (2.9 ) 2.8 22.0 21.9 Balance as of December 31, 2013 $ (0.3 ) $ (25.8 ) $ (17.5 ) $ (43.6 ) Other comprehensive income before reclassifications 0.9 (0.3 ) (10.2 ) (9.6 ) Amounts reclassified from accumulated other comprehensive income (0.3 ) 2.5 0.4 2.6 Net current-period other comprehensive income (loss) 0.6 2.2 (9.8 ) (7.0 ) Balance as of December 31, 2014 $ 0.3 $ (23.6 ) $ (27.3 ) $ (50.6 ) Other comprehensive income before reclassifications (0.5 ) (11.0 ) (5.0 ) (16.5 ) Amounts reclassified from accumulated other comprehensive income (0.3 ) 3.2 2.6 5.5 Net current-period other comprehensive income (loss) (0.8 ) (7.8 ) (2.4 ) (11.0 ) Allocation of AOCI to noncontrolling interest — 2.0 — 2.0 Distribution of CPG to shareholders (Note 3) — 13.9 10.6 24.5 Balance as of December 31, 2015 $ (0.5 ) $ (15.5 ) $ (19.1 ) $ (35.1 ) (1) All amounts are net of tax. Amounts in parentheses indicate debits.

Other, Net (Tables)

Other, Net (Tables)	12 Months Ended
	Dec. 31, 2015
Other Nonoperating Income (Expense) [Abstract]
Schedule Of Other, Net	Year Ended December 31, (in millions) 2015 2014 2013 Interest Income $ 0.8 $ 3.8 $ 3.5 AFUDC Equity 11.5 10.7 11.7 Charitable Contributions (4.8 ) (11.1 ) (8.2 ) Miscellaneous (1) 9.9 10.0 (0.2 ) Total Other, net $ 17.4 $ 13.4 $ 6.8 (1) Miscellaneous primarily consists of transmission upgrade agreement income in 2015 and 2014.

Interest Expense, Net (Tables)

Interest Expense, Net (Tables)	12 Months Ended
	Dec. 31, 2015
Interest Expense [Abstract]
Schedule Of Interest Expense, Net	Year Ended December 31, (in millions) 2015 2014 2013 Interest on long-term debt $ 377.5 $ 368.6 $ 364.4 Interest on short-term borrowings (1) 2.2 5.2 2.7 Debt discount/cost amortization 8.7 8.0 7.5 Accounts receivable securitization 2.5 2.9 2.7 Allowance for borrowed funds used and interest capitalized during construction (5.4 ) (5.3 ) (6.1 ) Other (5.3 ) 0.1 4.1 Total Interest Expense, net $ 380.2 $ 379.5 $ 375.3 (1) Refer to Note 15, "Short-Term Borrowings," for additional information.

Segments Of Business (Tables)

Segments Of Business (Tables)	12 Months Ended
	Dec. 31, 2015
Segment Reporting [Abstract]
Schedule Of Operating Income Derived From Revenues And Expenses By Segment	Year Ended December 31, (in millions) 2015 2014 2013 REVENUES Gas Distribution Operations Unaffiliated $ 3,068.7 $ 3,593.6 $ 3,053.5 Intersegment 0.4 0.3 0.3 Total 3,069.1 3,593.9 3,053.8 Electric Operations Unaffiliated 1,573.6 1,672.6 1,564.2 Intersegment 0.8 0.8 0.7 Total 1,574.4 1,673.4 1,564.9 Corporate and Other Unaffiliated 9.5 6.2 7.7 Intersegment 396.4 412.5 370.2 Total 405.9 418.7 377.9 Eliminations (397.6 ) (413.6 ) (371.2 ) Consolidated Revenues $ 4,651.8 $ 5,272.4 $ 4,625.4 Year Ended December 31, (in millions) 2015 2014 2013 Operating Income (Loss) Gas Distribution Operations $ 555.8 $ 537.0 $ 445.4 Electric Operations 264.4 282.7 265.5 Corporate and Other (20.3 ) (30.6 ) (12.8 ) Consolidated $ 799.9 $ 789.1 $ 698.1 Depreciation and Amortization Gas Distribution Operations $ 232.6 $ 217.6 $ 201.4 Electric Operations 267.7 244.4 244.4 Corporate and Other 24.1 24.9 24.6 Consolidated $ 524.4 $ 486.9 $ 470.4 Assets Gas Distribution Operations $ 10,094.5 $ 9,443.7 Electric Operations 5,265.3 5,009.9 Corporate and Other (1) 2,132.7 10,136.2 Consolidated $ 17,492.5 $ 24,589.8 Capital Expenditures (2) Gas Distribution Operations $ 917.0 $ 860.3 $ 790.8 Electric Operations 400.3 438.8 426.3 Corporate and Other 50.2 40.5 31.4 Consolidated $ 1,367.5 $ 1,339.6 $ 1,248.5 (1) The 2014 balances for Corporate and Other includes assets of Discontinued Operations refer to Note 3 "Discontinued Operations," for additional information. (2) Amounts differ from those presented on the Statements of Consolidated Cash Flows primarily due to the inclusion of capital expenditures included in current liabilities and AFUDC Equity.

Quarterly Financial Data (Table

Quarterly Financial Data (Tables)	12 Months Ended
	Dec. 31, 2015
Quarterly Financial Data [Abstract]
Schedule Of Quarterly Financial Data	(in millions, except per share data) First Quarter Second Quarter Third Quarter Fourth Quarter 2015 Gross revenues $ 1,852.2 $ 884.6 $ 817.2 $ 1,097.8 Operating Income 386.3 84.4 109.7 219.5 Income (Loss) from Continuing Operations 192.5 (73.1 ) 14.8 64.4 Results from Discontinued Operations - net of taxes (1) 82.8 45.4 (19.7 ) (5.0 ) Net Income (Loss) 275.3 (27.7 ) (4.9 ) 59.4 Net Income (Loss) attributable to NiSource 268.4 (36.4 ) (4.9 ) 59.4 Basic Earnings (Loss) Per Share Continuing Operations 0.61 (0.23 ) 0.05 0.20 Discontinued Operations 0.24 0.12 (0.07 ) (0.01 ) Basic Earnings (Loss) Per Share $ 0.85 $ (0.11 ) $ (0.02 ) $ 0.19 Diluted Earnings (Loss) Per Share Continuing Operations 0.61 (0.23 ) 0.05 0.20 Discontinued Operations 0.24 0.12 (0.07 ) (0.01 ) Diluted Earnings (Loss) Per Share $ 0.85 $ (0.11 ) $ (0.02 ) $ 0.19 2014 Gross revenues $ 2,017.2 $ 1,023.7 $ 838.2 $ 1,393.3 Operating Income 373.3 117.8 71.1 226.9 Income (Loss) from Continuing Operations 173.1 20.8 (17.2 ) 79.5 Results from Discontinued Operations - net of taxes (1) 93.1 57.4 48.6 74.7 Net Income 266.2 78.2 31.4 154.2 Net Income attributable to NiSource 266.2 78.2 31.4 154.2 Basic Earnings Per Share Continuing Operations 0.55 0.07 (0.05 ) 0.25 Discontinued Operations 0.30 0.18 0.15 0.24 Basic Earnings Per Share $ 0.85 $ 0.25 $ 0.10 $ 0.49 Diluted Earnings Per Share Continuing Operations 0.55 0.07 (0.05 ) 0.25 Discontinued Operations 0.30 0.18 0.15 0.24 Diluted Earnings Per Share $ 0.85 $ 0.25 $ 0.10 $ 0.49
Adjustments to Quarterly Financial Data for Discontinued Operations [Table Text Block]	(in millions) First Quarter Second Quarter Third Quarter Fourth Quarter 2015 Gross revenues $ 2,149.7 $ 1,169.0 Operating Income 530.1 165.1 Income (Loss) from Continuing Operations 275.3 (27.4 ) Results from Discontinued Operations - net of taxes $ — $ (0.3 ) 2014 Gross revenues $ 2,320.5 $ 1,335.1 $ 1,123.9 $ 1,691.1 Operating Income 533.7 219.6 157.8 351.3 Income from Continuing Operations 266.4 78.5 31.5 154.3 Results from Discontinued Operations - net of taxes $ (0.2 ) $ (0.3 ) $ (0.1 ) $ (0.1 )

Supplemental Cash Flow Inform57

Supplemental Cash Flow Information (Tables)	12 Months Ended
	Dec. 31, 2015
Supplemental Cash Flow Information [Abstract]
Schedule of Cash Flow, Supplemental Disclosures	Year Ended December 31, (in millions) 2015 2014 2013 Supplemental Disclosures of Cash Flow Information Non-cash transactions: Capital expenditures included in current liabilities $ 121.6 $ 127.4 $ 96.7 Assets acquired under a capital lease 47.5 76.7 28.4 Schedule of interest and income taxes paid: Cash paid for interest, net of interest capitalized amounts $ 390.4 $ 429.3 $ 402.7 Cash paid for income taxes 21.3 19.4 10.4

Valuation and Qualifying Acco58

Valuation and Qualifying Accounts (Tables)	12 Months Ended
	Dec. 31, 2015
Valuation and Qualifying Accounts [Abstract]
Schedule of Valuation and Qualifying Accounts Disclosure	N I S OURCE I NC . S CHEDULE II – V ALUATION AND Q UALIFYING ACCOUNTS Twelve months ended December 31, 2015 Additions ($ in millions) Balance Jan. 1, 2015 Charged to Costs and Expenses Charged to Other Account (1) Deductions for Purposes for which Reserves were Created Balance Dec. 31, 2015 Reserves Deducted in Consolidated Balance Sheet from Assets to Which They Apply: Reserve for accounts receivable $ 24.9 $ 22.5 $ 56.7 $ 83.8 $ 20.3 Reserve for other investments 3.0 — — — 3.0 Twelve months ended December 31, 2014 Additions ($ in millions) Balance Charged to Costs and Expenses Charged to Other Account (1) Deductions for Purposes for which Reserves were Created Balance Reserves Deducted in Consolidated Balance Sheet from Assets to Which They Apply: Reserve for accounts receivable $ 23.4 $ 21.8 $ 69.9 $ 90.2 $ 24.9 Reserve for other investments 3.0 — — — 3.0 Twelve months ended December 31, 2013 Additions ($ in millions) Balance Charged to Costs and Expenses Charged to Other Account (1) Deductions for Purposes for which Reserves were Created Balance Reserves Deducted in Consolidated Balance Sheet from Assets to Which They Apply: Reserve for accounts receivable $ 23.8 $ 13.8 $ 55.3 $ 69.5 $ 23.4 Reserve for other investments 3.0 — — — 3.0 (1) Charged to Other Accounts reflects the deferral of bad debt expense to a regulatory asset.

Nature Of Operations And Summ59

Nature Of Operations And Summary Of Significant Accounting Policies (Narrative) (Details) $ in Millions	12 Months Ended			132 Months Ended
	Dec. 31, 2015USD ($)shares	Dec. 31, 2014USD ($)shares	Dec. 31, 2013USD ($)shares	Dec. 31, 2015USD ($)
Basis Of Accounting Presentation [Line Items]
Number of customers	3,900,000
Restricted cash	$ 29.7	$ 24.9		$ 29.7
Unbilled revenue, less reserves	237.1	340.5		237.1
Other than Temporary Impairment Losses, Investments	$ 0	$ 0	$ 0
Pre-tax rate for allowance for funds used during construction	4.70%	4.50%	4.10%
Amortized software costs	$ 41.1	$ 33.7	$ 31.3
Unamortized software costs	167.1	162.3		167.1
Goodwill	$ 1,690.7	$ 1,690.7		1,690.7
Anti-dilutive shares | shares	0	0	0
Inventory valued using LIFO	$ 50.2	$ 55.1		50.2
Excess of replacement over LIFO value	(27.2)	(15.8)		(27.2)
Inventory valued using the weighted average cost methodology	$ 293.3	385.2		$ 293.3
Joint Ventures [Member]
Basis Of Accounting Presentation [Line Items]
Equity method investment percentage, minimum	3.00%			3.00%
NIPSCO [Member]
Basis Of Accounting Presentation [Line Items]
Unamortized Balance of Approved Sugar Creek Deferral	$ 14.3			$ 14.3
Sugar Creek Deferral Pending Approval	13.9			13.9
Columbia Of Ohio [Member]
Basis Of Accounting Presentation [Line Items]
Depreciation Before Rate Regulation	74.7			559.8
Decrease In Depreciation And Amortization Over That Reflected In Rates	7			66.4
Depreciation And Amortization Reflected In Rates	81.7			626.2
Depreciation Regulatory Asset	65.3	$ 72.3		65.3
Deferred Depreciation	38.5			38.5
Electric Operations [Member]
Basis Of Accounting Presentation [Line Items]
Goodwill	$ 0			$ 0

Nature Of Operations And Summ60

Nature Of Operations And Summary Of Significant Accounting Policies (Depreciation Provisions For Utility Plant As A Percentage Of The Original Cost) (Details)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Electric Operations [Member]
Basis Of Accounting Presentation [Line Items]
Depreciation provisions for utility plant, percentage	3.10%	3.00%	3.20%
Gas Distribution Operations [Member]
Basis Of Accounting Presentation [Line Items]
Depreciation provisions for utility plant, percentage	2.00%	2.10%	2.10%

Nature Of Operations And Summ61

Nature Of Operations And Summary Of Significant Accounting Policies (Computation Of Diluted Average Common Shares) (Details) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Diluted Average Common Shares Computation [Line Items]
Basic average common shares outstanding	317,746	315,120	312,402
Nonqualified stock options	0	6	80
Shares contingently issuable under employee stock plans	0	1,066	708
Shares restricted under stock plans	2,090	444	456
Diluted Average Common Shares	319,836	316,636	313,646

Discontinued Operations (Narrat

Discontinued Operations (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Jul. 01, 2015	May. 22, 2015
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Assets	$ 17,492.5	$ 24,589.8
Transaction Costs Related to Separation	55.4	23.7
Gain (Loss) on Disposition of Discontinued Operations - net of taxes	0	0	$ 34.9
Columbia Pipeline Group Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Assets	0			$ 9,200
Liabilities	0			5,600
Equity				$ 3,600
Unregulated Natural Gas Marketing Business [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (Loss) on Disposition of Discontinued Operations - net of taxes			(1.5)
Service Plan And Leasing Business Lines of Retail Services Business [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (Loss) on Disposition of Discontinued Operations - net of taxes			36.4
Columbia Pipeline Group [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Related Party Transaction, Other Revenues from Transactions with Related Party	$ 147.6	$ 146.2	$ 147.6
Columbia Pipeline Group [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Debt Instrument, Face Amount					$ 2,750

Discontinued Operations (Income

Discontinued Operations (Income Statement Disclosures) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015		Dec. 31, 2014		Dec. 31, 2013
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Disposal Group, Including Discontinued Operation, Natural Gas Midstream Revenue	$ 561.4		$ 1,034.3		$ 971.1
Disposal Group, Including Discontinued Operation, Other Revenue, Net	94.3		312.9		211.2
Disposal Group, Including Discontinued Operation, Revenue	655.7		1,347.2		1,182.3
Disposal Group, Including Discontinued Operation, Costs of Goods Sold	0.2		0.3		0.4
Disposal Group, Including Discontinued Operation, Gross Profit (Loss)	655.5		1,346.9		1,181.9
Disposal Group, Including Discontinued Operation, Utilities Operating Expense, Maintenance and Operations	375.8		769.1		619.5
Disposal Group, Including Discontinued Operation, Depreciation and Amortization	66.4		118.6		106.9
Disposal Group, Including Discontinued Operation, Impairment And Gain Loss On Sale Of Assets, Net	(13.6)		(34.5)		(18.6)
Disposal Group, Including Discontinued Operation, Taxes, Miscellaneous	38		67.1		62.2
Disposal Group, Including Discontinued Operation, Operating Expense	466.6		920.3		770
Disposal Group, Including Discontinued Operation, Income Loss From Equity Method Investments	29.1		46.6		35.9
Disposal Group, Including Discontinued Operation, Operating Income (Loss)	218		473.2		447.8
Disposal Group, Including Discontinued Operation, Interest Expense	(37.1)		(64.1)		(39.5)
Disposal Group, Including Discontinued Operation, Other Expense	8.2		7.9		26.5
Disposal Group, Including Discontinued Operation, Nonoperating Income Expense	(28.9)		(56.2)		(13)
Disposal Group, Including Discontinued Operation, Income Loss From Discontinued Operation Before Income Taxes Domestic	189.1		417		434.8
Disposal Group, Including Discontinued Operation, Income Tax Expense Benefit	85.6		143.2		158.6
Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	103.5		273.8		276.2
Gain on Disposition of Discontinued Operations - net of taxes	0		0		34.9
Columbia Pipeline Group Operations [Member] | Discontinued Operations, Disposed of by Means Other than Sale, Spinoff [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Disposal Group, Including Discontinued Operation, Natural Gas Midstream Revenue	561.4		1,034.3		971.1
Disposal Group, Including Discontinued Operation, Other Revenue, Net	94.3		312.9		208.7
Disposal Group, Including Discontinued Operation, Revenue	655.7		1,347.2		1,179.8
Disposal Group, Including Discontinued Operation, Costs of Goods Sold	0.2		0.3		0.4
Disposal Group, Including Discontinued Operation, Gross Profit (Loss)	655.5		1,346.9		1,179.4
Disposal Group, Including Discontinued Operation, Utilities Operating Expense, Maintenance and Operations	375.8	[1]	769.1	[1]	619.5	[2]
Disposal Group, Including Discontinued Operation, Depreciation and Amortization	66.4		118.6		106.9
Disposal Group, Including Discontinued Operation, Impairment And Gain Loss On Sale Of Assets, Net	(13.6)		(34.5)		(18.6)
Disposal Group, Including Discontinued Operation, Taxes, Miscellaneous	38		67.1		62.2
Disposal Group, Including Discontinued Operation, Operating Expense	466.6		920.3		770
Disposal Group, Including Discontinued Operation, Income Loss From Equity Method Investments	29.1		46.6		35.9
Disposal Group, Including Discontinued Operation, Operating Income (Loss)	218		473.2		445.3
Disposal Group, Including Discontinued Operation, Interest Expense	(37.1)		(64.1)		(39.5)
Disposal Group, Including Discontinued Operation, Other Expense	7.8		8.9		17.4
Disposal Group, Including Discontinued Operation, Nonoperating Income Expense	(29.3)		(55.2)		(22.1)
Disposal Group, Including Discontinued Operation, Income Loss From Discontinued Operation Before Income Taxes Domestic	188.7		418		423.2
Disposal Group, Including Discontinued Operation, Income Tax Expense Benefit	84.7		143.5		153.3
Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	104		274.5		269.9
Gain on Disposition of Discontinued Operations - net of taxes					0
Corporate and Other [Member] | Discontinued Operations, Disposed of by Means Other than Sale, Spinoff [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Disposal Group, Including Discontinued Operation, Natural Gas Midstream Revenue	0		0		0
Disposal Group, Including Discontinued Operation, Other Revenue, Net	0		0		2.5
Disposal Group, Including Discontinued Operation, Revenue	0		0		2.5
Disposal Group, Including Discontinued Operation, Costs of Goods Sold	0		0		0
Disposal Group, Including Discontinued Operation, Gross Profit (Loss)	0		0		2.5
Disposal Group, Including Discontinued Operation, Utilities Operating Expense, Maintenance and Operations	0		0		0
Disposal Group, Including Discontinued Operation, Depreciation and Amortization	0		0		0
Disposal Group, Including Discontinued Operation, Impairment And Gain Loss On Sale Of Assets, Net	0		0		0
Disposal Group, Including Discontinued Operation, Taxes, Miscellaneous	0		0		0
Disposal Group, Including Discontinued Operation, Operating Expense	0		0		0
Disposal Group, Including Discontinued Operation, Income Loss From Equity Method Investments	0		0		0
Disposal Group, Including Discontinued Operation, Operating Income (Loss)	0		0		2.5
Disposal Group, Including Discontinued Operation, Interest Expense	0		0		0
Disposal Group, Including Discontinued Operation, Other Expense	0.4		1		9.1
Disposal Group, Including Discontinued Operation, Nonoperating Income Expense	0.4		(1)		9.1
Disposal Group, Including Discontinued Operation, Income Loss From Discontinued Operation Before Income Taxes Domestic	0.4		(1)		11.6
Disposal Group, Including Discontinued Operation, Income Tax Expense Benefit	0.9		(0.3)		5.3
Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	(0.5)		(0.7)		6.3
Gain on Disposition of Discontinued Operations - net of taxes					34.9
Columbia Pipeline Group [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Related Party Transaction, Other Revenues from Transactions with Related Party	$ 147.6		$ 146.2		$ 147.6
[1]	Includes approximately $55.4 million of transaction costs related to the Separation.
[2]	Includes approximately $23.7 million of transaction costs related to the Separation.

Discontinued Operations (Balanc

Discontinued Operations (Balance Sheet Disclosures) (Details) - USD ($) $ in Millions		Dec. 31, 2015	Dec. 31, 2014
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Disposal Group, Including Discontinued Operation, Assets, Current		$ 0	$ 283.4
Disposal Group, Including Discontinued Operation, Assets, Noncurrent		0	7,546
Disposal Group, Including Discontinued Operation, Liabilities, Current		0.3	369
Disposal Group, Including Discontinued Operation, Liabilities, Noncurrent		$ 0	1,558.4
Columbia Pipeline Group Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Disposal Group, Including Discontinued Operation, Cash and Cash Equivalents			0.5
Disposal Group, Including Discontinued Operation, Accounts, Notes and Loans Receivable, Net			149.3
Disposal Group, Including Discontinued Operation, Inventory			4.8
Disposal Group, Including Discontinued Operation, Raw Materials and Supplies, Gross			24.9
Disposal Group, Including Discontinued Operation, Exchange Gas Receivable			34.8
Disposal Group, Including Discontinued Operation, Regulatory Assets, Current			6.1
Disposal Group, Including Discontinued Operation, Other Assets, Current			63
Disposal Group, Including Discontinued Operation, Assets, Current			283.4
Disposal Group, Including Discontinued Operation, Property, Plant and Equipment, Noncurrent			4,959.7
Disposal Group, Including Discontinued Operation, Goodwill, Noncurrent			1,975.5
Disposal Group, Including Discontinued Operation, Investments In Affiliates Subsidiaries Associates And Joint Ventures			444.3
Disposal Group, Including Discontinued Operation, Other Long Term Investments			5.6
Disposal Group, Including Discontinued Operation, Regulatory Assets, Noncurrent			151.9
Disposal Group, Including Discontinued Operation, Other Assets, Noncurrent			9
Disposal Group, Including Discontinued Operation, Assets, Noncurrent			7,546
Columbia Pipeline Group Operations [Member] | Discontinued Operations, Disposed of by Means Other than Sale, Spinoff [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Disposal Group, Including Discontinued Operation, Accounts Payable			60.5
Disposal Group, Including Discontinued Operation, Customer Deposits, Current			13.4
Disposal Group, Including Discontinued Operation, Accrued Income Tax Payable, Current			106.9
Disposal Group, Including Discontinued Operation, Exchange Gas Payable			34.7
Disposal Group, Including Discontinued Operation, Deferred Revenue, Current			22.2
Disposal Group, Including Discontinued Operation, Regulatory Liability, Current			1.3
Disposal Group, Including Discontinued Operation, Accrued Liability for Postretirement and Postemployment Benefits, Current			0.6
Disposal Group, Including Discontinued Operation, Legal and Environmental Reserves			1.5
Disposal Group, Including Discontinued Operation, Accrued Capital Expenditures			61.1
Disposal Group, Including Discontinued Operation, Other Liabilities, Current			66.8
Disposal Group, Including Discontinued Operation, Liabilities, Current			369
Disposal Group, Including Discontinued Operation, Deferred Tax Liabilities, Noncurrent			1,214.3
Disposal Group, Including Discontinued Operation, Deferred Investment Tax Credits, Noncurrent			0.2
Disposal Group, Including Discontinued Operation, Other Deferred Credits, Noncurrent			0.2
Disposal Group, Including Discontinued Operation, Pension and Other Postretirement and Postemployment Benefit Plans Liabilities, Noncurrent	[1]		(58)
Disposal Group, Including Discontinued Operation, Regulatory Liabilities, Noncurrent			294.2
Disposal Group, Including Discontinued Operation, Asset Retirement Obligations, Noncurrent			23.2
Disposal Group, Including Discontinued Operation, Other Liabilities, Noncurrent			84.3
Disposal Group, Including Discontinued Operation, Liabilities, Noncurrent			$ 1,558.4
[1]	Represents Columbia Pipeline Group segment's overfunded position in NiSource's net underfunded other postretirement plan.

Property, Plant And Equipment65

Property, Plant And Equipment (Schedule Of Property, Plant And Equipment) (Details) - USD ($) $ in Millions		Dec. 31, 2015	Dec. 31, 2014
Property, Plant and Equipment [Line Items]
Property Plant and Equipment		$ 18,988.1	$ 17,711.5
Accumulated Depreciation and Amortization		(6,876.6)	(6,654.1)
Net Property, Plant and Equipment		12,111.5	11,057.4
Gas Distribution Utility [Member]
Property, Plant and Equipment [Line Items]
Property Plant and Equipment	[1]	10,620.4	9,753.9
Accumulated Depreciation and Amortization	[1]	(3,029)	(2,922.7)
Electric Utility [Member]
Property, Plant and Equipment [Line Items]
Property Plant and Equipment	[1]	7,765.7	7,160
Accumulated Depreciation and Amortization	[1]	(3,767.7)	(3,596.5)
Common Utility [Member]
Property, Plant and Equipment [Line Items]
Property Plant and Equipment		107.2	181.5
Accumulated Depreciation and Amortization		(56.7)	(110.3)
Construction Work In Process [Member]
Property, Plant and Equipment [Line Items]
Property Plant and Equipment		453.6	573
Non-Utility And Other [Member]
Property, Plant and Equipment [Line Items]
Property Plant and Equipment		41.2	43.1
Accumulated Depreciation and Amortization		$ (23.2)	$ (24.6)
[1]	NIPSCO’s common utility plant and associated accumulated depreciation and amortization are allocated between Gas Distribution Utility and Electric Utility Property, Plant and Equipment.

Goodwill And Other Intangible66

Goodwill And Other Intangible Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Goodwill And Other Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	40 years
Goodwill	$ 1,690.7	$ 1,690.7
Amortization of Intangible Assets	11	11	$ 11
Intangible assets excluding goodwill	253.7	264.7
Amortization	188.5	$ 177.5
Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months	11
Finite-Lived Intangible Assets, Amortization Expense, Year Two	11
Finite-Lived Intangible Assets, Amortization Expense, Year Three	11
Finite-Lived Intangible Assets, Amortization Expense, Year Four	11
Finite-Lived Intangible Assets, Amortization Expense, Year Five	11
Gas Distribution Operations [Member]
Goodwill And Other Intangible Assets [Line Items]
Goodwill	1,690.7
Electric Operations [Member]
Goodwill And Other Intangible Assets [Line Items]
Goodwill	0
Corporate and Other [Member]
Goodwill And Other Intangible Assets [Line Items]
Goodwill	$ 0

Asset Retirement Obligations (C

Asset Retirement Obligations (Changes In Company's Liability For Asset Retirement Obligations) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014
Beginning Balance		$ 136.2	$ 148.1
Accretion recorded as a regulatory asset		8.6	8.2
Additions		6.5	0.3
Settlements		(7)	(2.2)
Change in estimated cash flows	[1]	109.7	(18.2)
Ending Balance		$ 254	$ 136.2
[1]	The change in estimated cash flows for 2015 is primarily attributable to estimated costs associated with the EPA's final rule for regulation of CCRs and changes to cost estimates for certain solid waste management units. See Note 18, "Other Commitments and Contingencies," for additional information on CCRs. The change in estimated cash flows for 2014 is primarily attributed to changes in estimated costs and settlement timing for electric generating stations and to retire pipeline.

Regulatory Matters (Narrative)

Regulatory Matters (Narrative) (Details) - USD ($) $ in Millions

May. 01, 2016

Feb. 28, 2016

Dec. 22, 2015

Nov. 04, 2015

Oct. 30, 2015

Oct. 07, 2015

Oct. 01, 2015

Sep. 17, 2015

Aug. 27, 2015

Aug. 07, 2015

Aug. 05, 2015

Apr. 30, 2015

Apr. 22, 2015

Apr. 16, 2015

Mar. 30, 2015

Mar. 19, 2015

Feb. 12, 2015

Dec. 17, 2014

Oct. 31, 2014

Sep. 12, 2014

Apr. 30, 2014

Nov. 12, 2013

Jul. 19, 2013

Dec. 31, 2015

Aug. 31, 2015

Aug. 21, 2015

Jul. 21, 2015

Feb. 27, 2015

Jan. 28, 2015

Nov. 25, 2014

Nov. 12, 2014

Jun. 30, 2014

Dec. 19, 2012

Regulatory Matters [Line Items]

Remaining Recovery Period of Regulatory Assets for which No Return on Investment During Recovery Period is Provided

41 years

Regulatory asset not earning return on investment

$ 1,668.7

Expenses recovered as components of cost of service and regulatory orders

1,544

Regulatory assets Requiring Specific Rate Action

262.7

Recorded Liability For Complaint

3.4

Seven Year Plan of Eligible Investments, Length of Plan

seven-year

Columbia Of Ohio [Member]

Regulatory Matters [Line Items]

Public Utilities, Approved Rate Increase (Decrease), Amount

$ 24.7

Requested Regulatory Deferral

$ 15

Approved Regulatory Deferral

$ 15

Regulatory Asset Deferral

11.6

Deferred Post-in-Service Carrying Charges, Depreciation Expense and Property Taxes

57.6

Columbia Of Pennsylvania [Member]

Regulatory Matters [Line Items]

Public Utilities, Requested Rate Increase (Decrease), Amount

$ 28

$ 46.2

Capital Investment Program Amount

197

Capital Investment Program Amount year 2

$ 220

Columbia Of Virginia [Member]

Regulatory Matters [Line Items]

Public Utilities, Approved Rate Increase (Decrease), Amount

$ 25.2

$ 31.8

NIPSCO [Member]

Regulatory Matters [Line Items]

Unamortized Balance of Approved Sugar Creek Deferral

14.3

Sugar Creek Deferral Pending Approval

13.9

Public Utilities, Requested Rate Increase (Decrease), Amount

$ 148

Investments for 2 Projects Authorized by the MISO

$ 450

Seven Year Plan of Eligible Investments Under TDSIC

$ 1,100

New Seven Year Plan of Eligible Investments under TDSIC

1,300

Annual Budget Approved

$ 18.6

Public Utilities, Approved Return on Equity, Percentage

12.38%

Public Utilities, Requested Return on Equity, Percentage

9.15%

Public Utilities, Requested Return on Equity, Percentage, Amended

8.67%

Public utilities, Approved Return on Equity, Percentage, Amended

10.32%

Columbia Of Massachusetts [Member]

Regulatory Matters [Line Items]

Public Utilities, Requested Rate Increase (Decrease), Amount

$ 49

$ 2.6

Public Utilities, Approved Rate Increase (Decrease), Amount

$ 32.8

Public Utilities, Requested Rate Increase (Decrease), Amended, Amount

$ 6.4

Projected Peak Undercollection

$ 3.6

Columbia Of Maryland [Member]

Regulatory Matters [Line Items]

Public Utilities, Requested Rate Increase (Decrease), Amount

$ 0.7

Public Utilities, Approved Rate Increase (Decrease), Amount

$ 0.5

TDSIC 3 Gas [Member] [Domain] | NIPSCO [Member]

Regulatory Matters [Line Items]

Regulatory Net Capital Expenditures Included In Filing

$ 75.2

Seven Year Plan of Eligible Investments Under TDSIC

$ 817

ECR 26 [Member] [Domain] | NIPSCO [Member]

Regulatory Matters [Line Items]

Regulatory Net Capital Expenditures Included In Filing

$ 800.7

$ 776.5

Flue Gas Desulfurization [Member] | NIPSCO [Member]

Regulatory Matters [Line Items]

Revised Capital Expenditure Estimate

255.3

Previously Approved Capital Expenditure Estimate

264.8

Revised MATS Capital Cost Estimate

48.6

Previously Approved MATS Capital Cost Estimate

$ 59.3

CMA Off-peak RDAF [Domain] | Columbia Of Massachusetts [Member]

Regulatory Matters [Line Items]

Public Utilities, Approved Rate Increase (Decrease), Amount

$ 2.5

CMA Peak Period RDAF [Domain] [Domain] | Columbia Of Massachusetts [Member]

Regulatory Matters [Line Items]

Public Utilities, Approved Rate Increase (Decrease), Amount

$ 17.1

CMA Off-Peak Local Distribution Adjustment Factor [Domain] | Columbia Of Massachusetts [Member]

Regulatory Matters [Line Items]

Public Utilities, Approved Rate Increase (Decrease), Amount

$ 70

CMA Peak-Period Local Distribution Adjustment Factor [Domain] | Columbia Of Massachusetts [Member]

Regulatory Matters [Line Items]

Public Utilities, Approved Rate Increase (Decrease), Amount

$ 49.7

TDSIC 1 Gas [Member] | NIPSCO [Member]

Regulatory Matters [Line Items]

Regulatory Net Capital Expenditures Included In Filing

$ 4.4

Seven Year Plan of Eligible Investments Under TDSIC

$ 840

TDSIC 2 Gas [Member] | NIPSCO [Member]

Regulatory Matters [Line Items]

Regulatory Net Capital Expenditures Included In Filing

$ 43.3

TDSIC 1 Electric [Member] | NIPSCO [Member]

Regulatory Matters [Line Items]

Regulatory Net Capital Expenditures Included In Filing

$ 19.4

Subsequent Event [Member]

Regulatory Matters [Line Items]

Public Utilities, Requested Rate Increase (Decrease), Cumulative Amount

$ 9

Subsequent Event [Member] | Columbia Of Ohio [Member]

Regulatory Matters [Line Items]

Public Utilities, Requested Rate Increase (Decrease), Amount

$ 33.2

Regulatory Matters (Regulatory

Regulatory Matters (Regulatory Assets) (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Regulatory Assets [Line Items]
Total Assets	$ 1,806.7	$ 1,763.9
Underrecovered gas and fuel costs	(34.8)	(32)
Total Regulatory Assets reflected in Current Regulatory Assets and Other Regulatory Assets	1,771.9	1,731.9
Unrecognized Pension Benefit And Other Postretirement Benefit Costs [Member]
Regulatory Assets [Line Items]
Total Assets	928.7	910.3
Other Postretirement Costs [Member]
Regulatory Assets [Line Items]
Total Assets	47	46.7
Environmental Costs [Member]
Regulatory Assets [Line Items]
Total Assets	62.2	65.9
Regulatory Effects Of Accounting For Income Taxes [Member]
Regulatory Assets [Line Items]
Total Assets	234.1	231.8
Underrecovered Gas And Fuel Costs [Member]
Regulatory Assets [Line Items]
Total Assets	34.8	32
Depreciation [Member]
Regulatory Assets [Line Items]
Total Assets	124.5	116.4
Uncollectible Accounts Receivable Deferred For Future Recovery [Member]
Regulatory Assets [Line Items]
Total Assets	17	26.1
Post-In Service Carrying Charges [Member]
Regulatory Assets [Line Items]
Total Assets	107.2	87.8
EERM Operation And Maintenance And Depreciation Deferral [Member]
Regulatory Assets [Line Items]
Total Assets	48.1	31.1
Sugar Creek Carrying Charges And Deferred Depreciation [Member]
Regulatory Assets [Line Items]
Total Assets	28.2	42.5
DSM Program [Member]
Regulatory Assets [Line Items]
Total Assets	35.6	37.9
Other Assets [Member]
Regulatory Assets [Line Items]
Total Assets	$ 139.3	$ 135.4

Regulatory Matters (Regulator70

Regulatory Matters (Regulatory Liabilities) (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Regulatory Liabilities [Line Items]
Total Liabilities	$ 1,581.8	$ 1,486.3
Less amounts included as Overrecovered gas and fuel cost	(148.1)	(45.6)
Total Regulatory Liabilities reflected in Current Regulatory Liabilities and Other Regulatory Liabilities and Other Removal Costs	1,433.7	1,440.7
Overrecovered Gas And Fuel Costs [Member]
Regulatory Liabilities [Line Items]
Total Liabilities	148.1	45.6
Cost Of Removal [Member]
Regulatory Liabilities [Line Items]
Total Liabilities	1,261.5	1,287
Regulatory Effects Of Accounting For Income Taxes [Member]
Regulatory Liabilities [Line Items]
Total Liabilities	34.2	42.3
Unrecognized Pension Benefit And Other Postretirement Benefit Costs [Member]
Regulatory Liabilities [Line Items]
Total Liabilities	8.1	10.1
Other Postretirement Costs [Member]
Regulatory Liabilities [Line Items]
Total Liabilities	38.8	31.9
Other Liabilities [Member]
Regulatory Liabilities [Line Items]
Total Liabilities	$ 91.1	$ 69.4

Variable Interest Entities (Nar

Variable Interest Entities (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Variable Interest Entity [Line Items]
Variable Interest Contract Period	10 years
Payments Pure Air	$ 19.5	$ 23

Income Taxes (Narrative) (Detai

Income Taxes (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 25, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Taxes [Line Items]
Outstanding Receivables and Operating Loss Carryforwards		$ 0.9
Reclassify Deferred Income Taxes from Current Assets to Noncurrent Liabilities			$ 272.1
Effective income tax rates		41.60%	39.40%	32.90%
Increase (Decrease) in Effective Tax Rate		2.20%	6.50%
Income Taxes Receivable			$ 6
Operating Loss Carryforwards		$ 29
Expected benefits to be realized		34.7	31.7
Tax Expense Recognized Due to Rate Change			7.1
Change In Unrecorded Tax Benefits		0.9
NOL Carryforwards Recognized From Remeasurement		2
Amortization Of Excess Tax Benefits		9.5	4.1	$ 1.4
Remaining carry forwards		395.4
Unrecognized tax benefits, if recognized, would affect effective tax rate		0.9	4.1	4
Unrecognized Tax Benefits Resulting in Net Operating Loss Carryforward		0	$ 0.2	$ 0.7
Changes to Liability for Uncertain Tax Positions		$ 0
Income Tax Rate Change Period			6 years
Tax Credit Carryforward, Expiration Date		Dec. 31, 2030
Deferred Tax Assets, Tax Credit Carryforwards, Alternative Minimum Tax		$ 7.3
Unrecognized Tax Benefits, Income Tax Penalties Accrued		0
Indiana State [Member] [Domain]
Income Taxes [Line Items]
Change in tax expense			$ 7.1
Columbia Of Pennsylvania [Member]
Income Taxes [Line Items]
Change in tax expense			5.4
Write Down of Charitable Contributions [Domain]
Income Taxes [Line Items]
Change in tax expense		17.8
Unamortized tax benefits		12
State Apportionment Changes and Permanent Items as a Result of Remeasurement [Domain]
Income Taxes [Line Items]
Change in tax expense		(10.5)	13.5
Corporate Restructuring [Member]
Income Taxes [Line Items]
Change in tax expense			$ 4.1
PATH and 50% Bonus Depreciation [Domain]
Income Taxes [Line Items]
Change in tax expense		$ 5.8
Minimum [Member]
Income Taxes [Line Items]
Tax Credit Carryforward, Expiration Date		Dec. 31, 2025
Maximum [Member]
Income Taxes [Line Items]
Tax Credit Carryforward, Expiration Date		Dec. 31, 2035
Previous [Member]
Income Taxes [Line Items]
Corporate Income Tax Rate	6.50%
Current [Member]
Income Taxes [Line Items]
Corporate Income Tax Rate	4.90%

Income Taxes (Schedule Of Compo

Income Taxes (Schedule Of Components Of Income Tax Expense) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Schedule of Income Tax Expense/Benefit [Line Items]
Current federal income taxes	$ 0	$ 0	$ (11.6)
Current state income taxes	6	5.4	1.8
Total current income taxes	6	5.4	(9.8)
Deferred federal income taxes	124.1	129.5	125.6
Deferred state income taxes	13.6	35.4	(3.4)
Total deferred income taxes	137.7	164.9	122.2
Deferred Investment Credits	(2.4)	(3.5)	(3.8)
Income Taxes from Continuing Operations	$ 141.3	$ 166.8	$ 108.6

Income Taxes (Schedule Of Reaso

Income Taxes (Schedule Of Reasons Behind Differences In Computation Of Total Income Taxes) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Schedule of Reasons Behind Differences in Computation of Total Income Taxes [Line Items]
Book income from Continuing Operations before income taxes	$ 339.9	$ 423	$ 329.6
Tax expense at statutory federal income tax rate, value	$ 118.9	$ 148.1	$ 115.4
Tax expense at statutory federal income tax rate, rate	35.00%	35.00%	35.00%
State income taxes, net of federal income tax benefit, value	$ 14.8	$ 15.7	$ 2.3
State income taxes, net of federal income tax benefit, rate	4.40%	3.70%	0.70%
Regulatory treatment of depreciation differences, value	$ 4.3	$ 0.7	$ (0.5)
Regulatory treatment of depreciation differences, rate	1.30%	0.20%	(0.20%)
Amortization of deferred investment tax credits, value	$ (2.4)	$ (3.5)	$ (3.8)
Amortization of deferred investment tax credits, rate	(0.70%)	(0.80%)	(1.20%)
Nondeductible expenses, value	$ 2.1	$ 0.8	$ 2.4
Nondeductible expenses, rate	0.60%	0.20%	0.70%
Employee Stock Ownership Plan Dividends, value	$ (2.9)	$ (3.8)	$ (3.6)
Employee Stock Ownership Plan Dividends, rate	(0.90%)	(0.90%)	(1.00%)
Regulatory treatment of AFUDC-Equity, value	$ (3.5)	$ (3.5)	$ (3.4)
Regulatory treatment of AFUDC-Equity, rate	(1.00%)	(0.80%)	(1.00%)
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Charitable Contributions, Amount	$ 17.8	$ 0	$ 0
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Charitable Contributions, Percent	5.20%	0.00%	0.00%
Effective Income Tax Rate Reconciliation, Other Adjustments, Percent	(2.30%)	2.80%	(0.10%)
Tax accrual adjustments and other, net, value	$ (7.8)	$ 12.3	$ (0.2)
Income Taxes from Continuing Operations	$ 141.3	$ 166.8	$ 108.6
Income Taxes from Continuing Operations, rate	41.60%	39.40%	32.90%

Income Taxes (Schedule Of Princ

Income Taxes (Schedule Of Principal Components Of Net Deferred Tax Liability) (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Schedule of Principal Components of Net Tax Expense [Line Items]
Accelerated depreciation and other property differences	$ 3,510.8	$ 2,964.6
Unrecovered gas and fuel costs	11.2	11.4
Other regulatory assets	403.3	610.6
Premiums and discounts associated with long-term debt	9.9	12.5
Total Deferred Tax Liabilities	3,935.2	3,599.1
Deferred investment tax credits and other regulatory liabilities	(74.4)	(79.3)
Cost of removal	(519.4)	(527.7)
Pension and other postretirement/postemployment benefits	(243.8)	(191.9)
Environmental liabilities	(45.9)	(52.1)
Net operating loss carryforward	(437.4)	(372.7)
Other accrued liabilities	(89)	(58.9)
Other, net	(160)	(150.7)
Total Deferred Tax Assets	(1,569.9)	(1,433.3)
Net Deferred Tax Liabilities less Deferred Tax Assets	$ 2,365.3	$ 2,165.8

Income Taxes (Schedule Of Recon

Income Taxes (Schedule Of Reconciliation Of The Beginning And Ending Amounts Of Unrecognized Tax Benefits) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Schedule Of Reconciliation Of The Beginning And Ending Amounts Of Unrecognized Tax Benefits [Line Items]
Unrecognized Tax Benefits-Opening Balance	$ 24.4	$ 23.7	$ 28.4
Gross increases-tax positions in prior period	0.4	0	1.6
Gross decreases-tax positions in prior period	(23.9)	(1)	(21.4)
Gross increases-current period tax positions	0	1.7	15.1
Unrecognized Tax Benefits-Ending Balance	0.9	24.4	23.7
Operating Loss Carryforwards	(0.9)	(24.2)	(23)
Balance-Net of Refunds and NOL Carryforwards	$ 0	$ 0.2	$ 0.7

Pension And Other Postretirem77

Pension And Other Postretirement Benefits (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015		Dec. 31, 2014		Dec. 31, 2013	Jul. 01, 2015
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		$ 1,973		$ 2,795.3
Regulatory assets		1,806.7		1,763.9
Regulatory liabilities		$ 1,581.8		1,486.3
Expected return on plan assets		8.30%
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		$ 1,747.1		2,330.3		$ 2,267.3
Defined Benefit Plan, Actuarial Gain (Loss)		(125.7)		(252.8)
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)		0.1		0.2		0.3
Defined Benefit Plan, Net Periodic Benefit Cost		25.4		10.4		78.7
Employer contributions		2.7		55.9
Expected contribution		3
Accumulated benefit obligation		2,190.5		2,732.3
Funded status of plan		459.6		421.1
Amortization of transition obligation		$ 0		$ 0		$ 0
Expected return on plan assets		8.30%		8.30%		8.30%
Defined Benefit Plan, Recognized Net (Gain) Loss Due to Settlements		$ (2.5)		$ 0		$ (33.4)
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		225.9		465		454.2
Defined Benefit Plan, Actuarial Gain (Loss)		45.2		(64)
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)		(5.2)		(4.3)		(0.7)
Defined Benefit Plan, Net Periodic Benefit Cost		1.3		(2.1)		24.8
Employer contributions		25.8		35.1
Decrease In Funded Status Other Postretirement Benefit Plans		(48.9)
Expected contribution		22.2
Funded status of plan		299.9		251
Amortization of transition obligation		$ 0		$ 0		$ 0.5
Expected return on plan assets		8.15%		8.14%		8.14%
Defined Benefit Plan, Recognized Net (Gain) Loss Due to Settlements		$ 0		$ 0		$ 0
Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		$ 95.3		$ 117		$ 124.7
Percentage of investments		5.00%		4.00%
Significant Unobservable Inputs (Level 3) [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		$ 0		$ 0
Unrecognized Pension Benefit And Other Postretirement Benefit Costs [Member]
Defined Benefit Plan Disclosure [Line Items]
Regulatory liabilities		8.1		10.1
Scenario, Forecast [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Actuarial Gain (Loss)	$ 61.2
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	0.2
Amortization of transition obligation	0
Scenario, Forecast [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Actuarial Gain (Loss)	3.1
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	4.9
Amortization of transition obligation	$ 0
Unrecognized Pension Benefit And Other Postretirement Benefit Costs [Member]
Defined Benefit Plan Disclosure [Line Items]
Regulatory assets		928.7		910.3
Columbia Pipeline Group [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Increase in funded status other postretirement benefit plans							$ 48
Columbia Pipeline Group [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Increase in funded status other postretirement benefit plans							$ 115.9
International Equities [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		323.2		420.5
International Equities [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		$ 39.6		$ 85.6
Commingled Funds [Member] | Short-Term Money Markets [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Notice Period		1 day		1 day
Commingled Funds [Member] | Short-Term Money Markets [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		$ 22.9	[1]	$ 32.6	[2]
Commingled Funds [Member] | Short-Term Money Markets [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		$ 2.4	[1]	$ 1.6	[2]
Commingled Funds [Member] | United States Equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Notice Period		3 days		3 days
Commingled Funds [Member] | United States Equities [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		$ 429.2	[1]	$ 957.2	[2]
Commingled Funds [Member] | United States Equities [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		14.3	[1]	29.8	[2]
Commingled Funds [Member] | International Equities [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		$ 210.1	[1]	$ 279.9	[2]
Commingled Funds [Member] | Fixed Income Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Notice Period		3 days		3 days
Maximum [Member] | Commingled Funds [Member] | International Equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Notice Period		30 days		30 days
Minimum [Member] | Commingled Funds [Member] | International Equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Notice Period		14 days		14 days
[1]	This class of investments is measured at fair value using the net asset value per share and has not been classified in the fair value hierarchy.
[2]	This class of investments is measured at fair value using the net asset value per share and has not been classified in the fair value hierarchy.

Pension And Other Postretirem78

Pension And Other Postretirement Benefits (Schedule Of Portfolio Asset Mix) (Details)	12 Months Ended
	Dec. 31, 2015
Domestic Equities [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Equities, Minimum	25.00%
Equities, Maximum	45.00%
Domestic Equities [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Equities, Minimum	35.00%
Equities, Maximum	55.00%
International Equities [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Equities, Minimum	15.00%
Equities, Maximum	25.00%
International Equities [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Equities, Minimum	15.00%
Equities, Maximum	25.00%
Fixed Income [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Equities, Minimum	23.00%
Equities, Maximum	37.00%
Fixed Income [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Equities, Minimum	20.00%
Equities, Maximum	50.00%
Real Estate/Private Equity/Hedge Funds [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Equities, Minimum	0.00%
Equities, Maximum	15.00%
Real Estate/Private Equity/Hedge Funds [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Equities, Minimum	0.00%
Equities, Maximum	0.00%
Short-Term Investments [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Equities, Minimum	0.00%
Equities, Maximum	10.00%
Short-Term Investments [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Equities, Minimum	0.00%
Equities, Maximum	10.00%

Pension And Other Postretirem79

Pension And Other Postretirement Benefits (Schedule Of Pension Plan And Postretirement Plan Asset Mix) (Details) - USD ($) $ in Millions	Dec. 31, 2015		Dec. 31, 2014		Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	$ 1,973		$ 2,795.3
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	$ 1,747.1		$ 2,330.3		$ 2,267.3
Percentage of total asset	100.00%		100.00%
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	$ 225.9		$ 465		$ 454.2
Percentage of total asset	100.00%		100.00%
Domestic Equities [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	$ 686.3		$ 957.2
Percentage of total asset	39.30%		41.10%
Domestic Equities [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	$ 105		$ 219.6
Percentage of total asset	46.50%		47.20%
International Equities [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	$ 323.2		$ 420.5
Percentage of total asset	18.50%		18.10%
International Equities [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	$ 39.6		$ 85.6
Percentage of total asset	17.50%		18.40%
Fixed Income [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	$ 619.3		$ 802.4
Percentage of total asset	35.50%		34.40%
Fixed Income [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	$ 79.1		$ 158.6
Percentage of total asset	35.00%		34.10%
Real Estate/Private Equity/Hedge Funds [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	$ 96.7		$ 117.6
Percentage of total asset	5.50%		5.00%
Real Estate/Private Equity/Hedge Funds [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	$ 0		$ 0
Percentage of total asset	0.00%		0.00%
Cash/Other [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	$ 21.6		$ 32.6
Percentage of total asset	1.20%		1.40%
Cash/Other [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	$ 2.2		$ 1.2
Percentage of total asset	1.00%		0.30%
Commingled Funds [Member] | Short-Term Money Markets [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	$ 22.9	[1]	$ 32.6	[2]
Commingled Funds [Member] | Short-Term Money Markets [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	2.4	[1]	1.6	[2]
Commingled Funds [Member] | International Equities [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	210.1	[1]	279.9	[2]
Commingled Funds [Member] | Fixed Income [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	302.5	[1]	409	[2]
Commingled Funds [Member] | United States Equities [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	429.2	[1]	957.2	[2]
Commingled Funds [Member] | United States Equities [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	$ 14.3	[1]	$ 29.8	[2]
[1]	This class of investments is measured at fair value using the net asset value per share and has not been classified in the fair value hierarchy.
[2]	This class of investments is measured at fair value using the net asset value per share and has not been classified in the fair value hierarchy.

Pension And Other Postretirem80

Pension And Other Postretirement Benefits (Schedule Of Fair Value Of Pension Plan Assets) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015		Dec. 31, 2014		Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Net Asset Value Excluded From Fair Value By Input	$ 981.4		$ 1,710.1
Defined Benefit Plan, Fair Value of Plan Assets	1,973		2,795.3
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	0		0
Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	734		689.6
Significant Other Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	160.4		274.1
Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	95.3		117		$ 124.7
Due To Brokers Net [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0.2	[1]	0.6	[2]
Accrued Investment Income Dividends [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets			4.6
Receivables/Payables [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	2.1		0.5
Fixed Income Securities [Member] | Other Fixed Income [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0.1		0.6		0
Fixed Income Securities [Member] | Mortgages/Asset Backed Securities [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets			0		0.1
Commingled Funds [Member] | International Equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Net Asset Value Excluded From Fair Value By Input	210.1		279.9
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	0		0
Commingled Funds [Member] | United States Equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Net Asset Value Excluded From Fair Value By Input	$ 443.5		$ 987
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Notice Period	3 days		3 days
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	$ 0		$ 0
Commingled Funds [Member] | Short-Term Money Markets [Member]
Defined Benefit Plan Disclosure [Line Items]
Net Asset Value Excluded From Fair Value By Input	$ 25.3		$ 34.2
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Notice Period	1 day		1 day
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	$ 0		$ 0
Commingled Funds [Member] | Fixed Income Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Net Asset Value Excluded From Fair Value By Input	$ 302.5		$ 409
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Notice Period	3 days		3 days
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	$ 0		$ 0
Private Equity Limited Partnerships [Member] | U.S. Multi-Strategy [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	46.4		56.2		57.9
Private Equity Limited Partnerships [Member] | International Multi-Strategy [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	29.3		35.3		38.2
Private Equity Limited Partnerships [Member] | Distressed Opportunities [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	5.9		7.6		8.9
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	1,747.1		2,330.3		2,267.3
Defined Benefit Plan Fair Value Of Plan Assets Before Pending Items	1,745.2		2,325.8
Pension Plan [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan Fair Value Of Plan Assets Before Pending Items	524.8		256
Pension Plan [Member] | Significant Other Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan Fair Value Of Plan Assets Before Pending Items	160.4		274.1
Pension Plan [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan Fair Value Of Plan Assets Before Pending Items	95.3		117
Pension Plan [Member] | Cash [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	7		17.1
Pension Plan [Member] | Cash [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	7		17.1
Pension Plan [Member] | Cash [Member] | Significant Other Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0		0
Pension Plan [Member] | Cash [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0		0
Pension Plan [Member] | International Equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	323.2		420.5
Pension Plan [Member] | Fixed Income [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	619.3		802.4
Pension Plan [Member] | Equity Securities [Member] | International Equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	45.3		134.5
Pension Plan [Member] | Equity Securities [Member] | International Equities [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	45.3		133.9
Pension Plan [Member] | Equity Securities [Member] | International Equities [Member] | Significant Other Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0		0.6
Pension Plan [Member] | Equity Securities [Member] | International Equities [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0		0
Pension Plan [Member] | Equity Securities [Member] | United States Equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets			0.4
Pension Plan [Member] | Equity Securities [Member] | United States Equities [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets			0.4
Pension Plan [Member] | Equity Securities [Member] | United States Equities [Member] | Significant Other Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets			0
Pension Plan [Member] | Equity Securities [Member] | United States Equities [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets			0
Pension Plan [Member] | Fixed Income Securities [Member] | Government [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	64.6		118.4
Pension Plan [Member] | Fixed Income Securities [Member] | Government [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0		104.6
Pension Plan [Member] | Fixed Income Securities [Member] | Government [Member] | Significant Other Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	64.6		13.8
Pension Plan [Member] | Fixed Income Securities [Member] | Government [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0		0
Pension Plan [Member] | Fixed Income Securities [Member] | Corporate [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	95.8		257
Pension Plan [Member] | Fixed Income Securities [Member] | Corporate [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0		0
Pension Plan [Member] | Fixed Income Securities [Member] | Corporate [Member] | Significant Other Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	95.8		257
Pension Plan [Member] | Fixed Income Securities [Member] | Corporate [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0		0
Pension Plan [Member] | Fixed Income Securities [Member] | Other Fixed Income [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0.1		0.6
Pension Plan [Member] | Fixed Income Securities [Member] | Other Fixed Income [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0		0
Pension Plan [Member] | Fixed Income Securities [Member] | Other Fixed Income [Member] | Significant Other Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0		0
Pension Plan [Member] | Fixed Income Securities [Member] | Other Fixed Income [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0.1		0.6
Pension Plan [Member] | Fixed Income Securities [Member] | Mortgages/Asset Backed Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets			2.7
Pension Plan [Member] | Fixed Income Securities [Member] | Mortgages/Asset Backed Securities [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets			0
Pension Plan [Member] | Fixed Income Securities [Member] | Mortgages/Asset Backed Securities [Member] | Significant Other Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets			2.7
Pension Plan [Member] | Fixed Income Securities [Member] | Mortgages/Asset Backed Securities [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets			0
Pension Plan [Member] | Commingled Funds [Member] | International Equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	210.1	[3]	279.9	[4]
Pension Plan [Member] | Commingled Funds [Member] | Fixed Income [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	302.5	[3]	409	[4]
Pension Plan [Member] | Commingled Funds [Member] | United States Equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	429.2	[3]	957.2	[4]
Pension Plan [Member] | Commingled Funds [Member] | Short-Term Money Markets [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	22.9	[3]	32.6	[4]
Pension Plan [Member] | Private Equity Limited Partnerships [Member] | U.S. Multi-Strategy [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	46.4	[5]	56.2	[6]
Pension Plan [Member] | Private Equity Limited Partnerships [Member] | U.S. Multi-Strategy [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0	[5]	0	[6]
Pension Plan [Member] | Private Equity Limited Partnerships [Member] | U.S. Multi-Strategy [Member] | Significant Other Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0	[5]	0	[6]
Pension Plan [Member] | Private Equity Limited Partnerships [Member] | U.S. Multi-Strategy [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	46.4	[5]	56.2	[6]
Pension Plan [Member] | Private Equity Limited Partnerships [Member] | International Multi-Strategy [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	29.3	[7]	35.3	[8]
Pension Plan [Member] | Private Equity Limited Partnerships [Member] | International Multi-Strategy [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0	[7]	0	[8]
Pension Plan [Member] | Private Equity Limited Partnerships [Member] | International Multi-Strategy [Member] | Significant Other Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0	[7]	0	[8]
Pension Plan [Member] | Private Equity Limited Partnerships [Member] | International Multi-Strategy [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	29.3	[7]	35.3	[8]
Pension Plan [Member] | Private Equity Limited Partnerships [Member] | Distressed Opportunities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	5.9		7.6
Pension Plan [Member] | Private Equity Limited Partnerships [Member] | Distressed Opportunities [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0		0
Pension Plan [Member] | Private Equity Limited Partnerships [Member] | Distressed Opportunities [Member] | Significant Other Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0		0
Pension Plan [Member] | Private Equity Limited Partnerships [Member] | Distressed Opportunities [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	5.9		7.6
Pension Plan [Member] | Real Estate [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	13.6		17.3
Pension Plan [Member] | Real Estate [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0		0
Pension Plan [Member] | Real Estate [Member] | Significant Other Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0		0
Pension Plan [Member] | Real Estate [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	13.6		17.3
Pension Plan [Member] | Mutual Funds [Member] | International Equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	64.9
Pension Plan [Member] | Mutual Funds [Member] | International Equities [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	64.9
Pension Plan [Member] | Mutual Funds [Member] | U.S. Multi-Strategy [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	257.1
Pension Plan [Member] | Mutual Funds [Member] | U.S. Multi-Strategy [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	257.1
Pension Plan [Member] | Mutual Funds [Member] | Fixed Income [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	150.5
Pension Plan [Member] | Mutual Funds [Member] | Fixed Income [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	150.5
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	225.9		465		$ 454.2
Other Postretirement Benefits [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	209.2		433.6
Other Postretirement Benefits [Member] | Significant Other Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0		0
Other Postretirement Benefits [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0		0
Other Postretirement Benefits [Member] | International Equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	39.6		85.6
Other Postretirement Benefits [Member] | Fixed Income [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	79.1		158.6
Other Postretirement Benefits [Member] | Commingled Funds [Member] | United States Equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	14.3	[3]	29.8	[4]
Other Postretirement Benefits [Member] | Commingled Funds [Member] | Short-Term Money Markets [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	2.4	[3]	1.6	[4]
Other Postretirement Benefits [Member] | Mutual Funds [Member] | International Equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	41.4		85.6
Other Postretirement Benefits [Member] | Mutual Funds [Member] | International Equities [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	41.4		85.6
Other Postretirement Benefits [Member] | Mutual Funds [Member] | International Equities [Member] | Significant Other Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0		0
Other Postretirement Benefits [Member] | Mutual Funds [Member] | International Equities [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0		0
Other Postretirement Benefits [Member] | Mutual Funds [Member] | Fixed Income [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	78		158.2
Other Postretirement Benefits [Member] | Mutual Funds [Member] | Fixed Income [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	78		158.2
Other Postretirement Benefits [Member] | Mutual Funds [Member] | Fixed Income [Member] | Significant Other Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0		0
Other Postretirement Benefits [Member] | Mutual Funds [Member] | Fixed Income [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0		0
Other Postretirement Benefits [Member] | Mutual Funds [Member] | United States Equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	89.8		189.8
Other Postretirement Benefits [Member] | Mutual Funds [Member] | United States Equities [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	89.8		189.8
Other Postretirement Benefits [Member] | Mutual Funds [Member] | United States Equities [Member] | Significant Other Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	0		0
Other Postretirement Benefits [Member] | Mutual Funds [Member] | United States Equities [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	$ 0		$ 0
[1]	This class represents pending trades with brokers.
[2]	This class represents pending trades with brokers.
[3]	This class of investments is measured at fair value using the net asset value per share and has not been classified in the fair value hierarchy.
[4]	This class of investments is measured at fair value using the net asset value per share and has not been classified in the fair value hierarchy.
[5]	This class includes limited partnerships/fund of funds that invest in a diverse portfolio of private equity strategies, including buy-outs, venture capital, growth capital, special situations and secondary markets, primarily inside the United States.
[6]	This class includes limited partnerships/fund of funds that invest in a diverse portfolio of private equity strategies, including buy-outs, venture capital, growth capital, special situations and secondary markets, primarily in the United States.
[7]	This class includes limited partnerships/fund of funds that invest in diverse portfolio of private equity strategies, including buy-outs, venture capital, growth capital, special situations and secondary markets, primarily outside the United States.
[8]	This class includes limited partnerships/fund of funds that invest in a diverse portfolio of private equity strategies, including buy-outs, venture capital, growth capital, special situations and secondary markets, primarily outside the United States.

Pension And Other Postretirem81

Pension And Other Postretirement Benefits (Schedule Of Changes In The Fair Value Of The Plan Level Three Assets) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of year	$ 2,795.3
Fair value of plan assets at end of year	1,973	$ 2,795.3
Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of year	117	124.7
Total gains or losses (unrealized / realized)	(6.8)	5.4
Purchases	1.3	3.5
(Sales)	(16.2)	(16.6)
Transfers into/(out of) level 3	0	0
Fair value of plan assets at end of year	95.3	117
Real Estate [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of year	17.3	19.6
Total gains or losses (unrealized / realized)		2.3
Purchases		0.1
(Sales)		(4.7)
Transfers into/(out of) level 3		0
Fair value of plan assets at end of year		17.3
Private Equity Limited Partnerships [Member] | U.S. Multi-Strategy [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of year	56.2	57.9
Total gains or losses (unrealized / realized)	(3.5)	2.7
Purchases	1.1	2.5
(Sales)	(7.4)	(6.9)
Transfers into/(out of) level 3	0	0
Fair value of plan assets at end of year	46.4	56.2
Private Equity Limited Partnerships [Member] | International Multi-Strategy [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of year	35.3	38.2
Total gains or losses (unrealized / realized)	(2.3)	(0.4)
Purchases	0.1	0.5
(Sales)	(3.8)	(3)
Transfers into/(out of) level 3	0	0
Fair value of plan assets at end of year	29.3	35.3
Private Equity Limited Partnerships [Member] | Distressed Opportunities [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of year	7.6	8.9
Total gains or losses (unrealized / realized)	(0.5)	0.5
Purchases	0	0.1
(Sales)	(1.2)	(1.9)
Transfers into/(out of) level 3	0	0
Fair value of plan assets at end of year	5.9	7.6
Private Equity Limited Partnerships [Member] | Real Estate [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of year	17.3
Total gains or losses (unrealized / realized)	(0.5)
Purchases	0.1
(Sales)	(3.3)
Transfers into/(out of) level 3	0
Fair value of plan assets at end of year	13.6	17.3
Fixed Income Securities [Member] | Mortgages/Asset Backed Securities [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of year	0	0.1
Total gains or losses (unrealized / realized)		0
Purchases		0
(Sales)		(0.1)
Transfers into/(out of) level 3		0
Fair value of plan assets at end of year		0
Fixed Income Securities [Member] | Other Fixed Income [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of year	0.6	0
Total gains or losses (unrealized / realized)	0	0.3
Purchases	0	0.3
(Sales)	(0.5)	0
Transfers into/(out of) level 3	0	0
Fair value of plan assets at end of year	$ 0.1	$ 0.6

Pension And Other Postretirem82

Pension And Other Postretirement Benefits Pension and Other Postretirement Benefits (Schedule of Net Asset Value Per Share) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Net Asset Value Excluded From Fair Value By Input	$ 981.4	$ 1,710.1
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	0	0
Commingled Funds [Member] | Short-Term Money Markets [Member]
Defined Benefit Plan Disclosure [Line Items]
Net Asset Value Excluded From Fair Value By Input	25.3	34.2
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	$ 0	$ 0
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Frequency	Daily	Daily
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Notice Period	1 day	1 day
Commingled Funds [Member] | United States Equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Net Asset Value Excluded From Fair Value By Input	$ 443.5	$ 987
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	$ 0	$ 0
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Frequency	Monthly	Monthly
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Notice Period	3 days	3 days
Commingled Funds [Member] | International Equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Net Asset Value Excluded From Fair Value By Input	$ 210.1	$ 279.9
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	$ 0	$ 0
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Frequency	Monthly	Monthly
Commingled Funds [Member] | Fixed Income Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Net Asset Value Excluded From Fair Value By Input	$ 302.5	$ 409
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	$ 0	$ 0
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Frequency	Monthly	Monthly
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Notice Period	3 days	3 days
Minimum [Member] | Commingled Funds [Member] | International Equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Notice Period	14 days	14 days
Maximum [Member] | Commingled Funds [Member] | International Equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Investment Redemption, Notice Period	30 days	30 days

Pension And Other Postretirem83

Pension And Other Postretirement Benefits (Schedule Of Reconciliation Of The Plans Funded Status And Amounts Reflected) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014		Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of year		$ 2,795.3
Fair value of plan assets at end of year		1,973	$ 2,795.3
Noncurrent liabilities		(299.3)	(250.4)
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation at beginning of year	[1]	2,751.4	2,528.2
Service cost		34.8	34.8		$ 36.4
Interest cost		95.9	109		98.9
Plan participants' contributions		0	0
Plan amendments		0	0.6
Actuarial loss (gain)		(91.7)	272.1
Settlement Loss		0.5	0
Benefits paid		(171.8)	(193.3)
Estimated benefits paid by incurred subsidy		0	0
Projected Benefit Obligation Change Due to Separation		(412.4)	0
Plan Assets Change Due to Separation		(364.4)	0
Projected benefit obligation at end of year		2,206.7	2,751.4	[1]	2,528.2	[1]
Fair value of plan assets at beginning of year		2,330.3	2,267.3
Actual return on plan assets		(49.7)	200.4
Employer contributions		2.7	55.9
Fair value of plan assets at end of year		1,747.1	2,330.3		2,267.3
Funded Status at end of year		(459.6)	(421.1)
Current liabilities		(3)	(3.5)
Noncurrent liabilities		(456.6)	(417.6)
Net amount recognized at end of year	[2]	(459.6)	(421.1)
Unrecognized prior service cost	[3]	0.7	(3.5)
Unrecognized actuarial loss	[3]	925.6	1,009.8
Defined Benefit Plan Amounts Recognized In Other Comprehensive Income Or Regulatory Asset Or Liability	[3]	926.3	1,006.3
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation at beginning of year	[1]	716	714.2
Service cost		6.4	8.5		12.1
Interest cost		24.9	30.1		32.2
Plan participants' contributions		7.3	9.1
Plan amendments		0.1	(41.5)
Actuarial loss (gain)		(71.5)	47.6
Settlement Loss		0	0
Benefits paid		(43.7)	(53.7)
Estimated benefits paid by incurred subsidy		0.8	1.7
Projected Benefit Obligation Change Due to Separation		(114.5)	0
Plan Assets Change Due to Separation		(230.4)	0
Projected benefit obligation at end of year		525.8	716	[1]	714.2	[1]
Fair value of plan assets at beginning of year		465	454.2
Actual return on plan assets		1.9	20.3
Employer contributions		25.8	35.1
Fair value of plan assets at end of year		225.9	465		$ 454.2
Funded Status at end of year		(299.9)	(251)
Current liabilities		(0.6)	(0.6)
Net amount recognized at end of year	[2]	(299.9)	(251)
Unrecognized prior service cost	[3]	(41.6)	(49.2)
Unrecognized actuarial loss	[3]	66.1	95.5
Defined Benefit Plan Amounts Recognized In Other Comprehensive Income Or Regulatory Asset Or Liability	[3]	$ 24.5	$ 46.3
[1]	The change in benefit obligation for Pension Benefits represents the change in Projected Benefit Obligation while the change in benefit obligation for Other Postretirement Benefits represents the change in Accumulated Postretirement Benefit Obligation.
[2]	NiSource recognizes in its Consolidated Balance Sheets the underfunded and overfunded status of its various defined benefit postretirement plans, measured as the difference between the fair value of the plan assets and the benefit obligation.
[3]	NiSource determined that for certain rate-regulated subsidiaries the future recovery of pension and other postretirement benefits costs is probable. These rate-regulated subsidiaries recorded regulatory assets and liabilities of $928.7 million and $8.1 million, respectively, as of December 31, 2015, and $910.3 million and $10.1 million, respectively, as of December 31, 2014 that would otherwise have been recorded to accumulated other comprehensive loss.

Pension And Other Postretirem84

Pension And Other Postretirement Benefits (Schedule Of Significant Actuarial Assumptions In Determining Funded Status Plan) (Details)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount Rate	4.24%	3.81%
Rate of Compensation Increases	4.00%	4.00%
Trend for Next Year	0.00%	0.00%
Ultimate Trend	0.00%	0.00%
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount Rate	4.33%	3.94%
Rate of Compensation Increases	0.00%	0.00%
Trend for Next Year	8.41%	6.90%
Ultimate Trend	4.50%	4.50%
Year Ultimate Trend Reached	2,022	2,021

Pension And Other Postretirem85

Pension And Other Postretirement Benefits (Schedule Of One-Percentage-Point Change In Assumed Health Care Cost Trend Rates) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2015USD ($)
Defined Benefit Plan Disclosure [Line Items]
Effect on service and interest components of net periodic cost, 1% point increase	$ 1.7
Effect on service and interest components of net periodic cost, 1% point decrease	(1.5)
Effect on accumulated postretirement benefit obligation, 1% point increase	32.4
Effect on accumulated postretirement benefit obligation, 1% point decrease	$ (28)

Pension And Other Postretirem86

Pension And Other Postretirement Benefits (Schedule Of Expected Payments To Participants In Pension Plan) (Details) $ in Millions	Dec. 31, 2015USD ($)
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
2,015	$ 174.1
2,016	175.8
2,017	177.1
2,018	176.1
2,019	174.5
2020-2024	837.8
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
2,015	34.7
2,016	35.4
2,017	36
2,018	36.7
2,019	37
2020-2024	181.5
Postretirement Health Coverage [Member]
Defined Benefit Plan Disclosure [Line Items]
2,015	0.9
2,016	0.9
2,017	0.9
2,018	0.9
2,019	0.9
2020-2024	$ 3.6

Pension And Other Postretirem87

Pension And Other Postretirement Benefits (Components Of The Plans' Net Periodic Benefits Cost) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost	$ 34.8	$ 34.8	$ 36.4
Interest cost	95.9	109	98.9
Expected return on assets	(167.2)	(181.1)	(168.1)
Amortization of transition obligation	0	0	0
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	0.1	0.2	0.3
Recognized actuarial loss	59.3	47.5	77.8
Net Periodic Benefit Costs	22.9	10.4	45.3
Settlement loss	2.5	0	33.4
Total Net Periodic Benefits Cost	25.4	10.4	78.7
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service Cost	6.4	8.5	12.1
Interest cost	24.9	30.1	32.2
Expected return on assets	(28.2)	(36.8)	(30.3)
Amortization of transition obligation	0	0	0.5
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	(5.2)	(4.3)	(0.7)
Recognized actuarial loss	3.4	0.4	11
Net Periodic Benefit Costs	1.3	(2.1)	24.8
Settlement loss	0	0	0
Total Net Periodic Benefits Cost	$ 1.3	$ (2.1)	$ 24.8

Pension And Other Postretirem88

Pension And Other Postretirement Benefits (Schedule Of Key Assumptions That Were Used To Calculate The Net Periodic Benefits Cost) (Details)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Expected Long-Term Rate of Return on Plan Assets	8.30%
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount Rate	3.81%	4.50%	3.63%
Expected Long-Term Rate of Return on Plan Assets	8.30%	8.30%	8.30%
Rate of Compensation Increases	4.00%	4.00%	4.00%
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount Rate	3.94%	4.75%	3.95%
Expected Long-Term Rate of Return on Plan Assets	8.15%	8.14%	8.14%
Rate of Compensation Increases	0.00%	0.00%	0.00%

Pension And Other Postretirem89

Pension And Other Postretirement Benefits (Schedule Of Changes In Plan Assets And Projected Benefit Obligations Recognized In Other Comprehensive Income) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Pension Plan [Member]
Net prior service cost/(credit)	$ 0	$ 0.6
Net actuarial (gain)/loss	125.7	252.8
Settlements	(2.5)	0	$ (33.4)
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	(0.1)	(0.2)	(0.3)
Less: amortization of net actuarial (gain) loss	(59.3)	(47.5)	(77.8)
Defined Benefit Plan Change Due to Separation	(143.8)	0
Total Recognized in Other Comprehensive Income or Regulatory Asset or Liability	(80)	205.7
Amount Recognized in Net Periodic Benefits Cost and Other Comprehensive Income or Regulatory Asset or Liability	(54.6)	216.1
Other Postretirement Benefits [Member]
Net prior service cost/(credit)	0.1	(41.5)
Net actuarial (gain)/loss	(45.2)	64
Settlements	0	0	0
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	5.2	4.3	0.7
Less: amortization of net actuarial (gain) loss	(3.4)	(0.4)	$ (11)
Defined Benefit Plan Change Due to Separation	21.5	0
Total Recognized in Other Comprehensive Income or Regulatory Asset or Liability	(21.8)	26.4
Amount Recognized in Net Periodic Benefits Cost and Other Comprehensive Income or Regulatory Asset or Liability	$ (20.5)	$ 24.3

Authorized Classes Of Cumulat90

Authorized Classes Of Cumulative Preferred And Preference Stocks (Details)	Dec. 31, 2015$ / sharesshares
Authorized Classes Of Cumulative Preferred And Preference Stocks [Line Items]
Number of shares authorized	20,000,000
Par value of shares | $ / shares	$ 0.01
Shares outstanding	0
NIPSCO [Member]
Authorized Classes Of Cumulative Preferred And Preference Stocks [Line Items]
Shares outstanding	0
Series A Junior Participating Preferred Shares [Member]
Authorized Classes Of Cumulative Preferred And Preference Stocks [Line Items]
Number of shares authorized	4,000,000
Cumulative Preferred With A 100 Par Value [Member] | NIPSCO [Member]
Authorized Classes Of Cumulative Preferred And Preference Stocks [Line Items]
Number of shares authorized	2,400,000
Par value of shares | $ / shares	$ 100
Cumulative Preferred With No Par Value [Member] | NIPSCO [Member]
Authorized Classes Of Cumulative Preferred And Preference Stocks [Line Items]
Number of shares authorized	3,000,000
Par value of shares | $ / shares	$ 0
Cumulative Preference With 50 As Par Value [Member] | NIPSCO [Member]
Authorized Classes Of Cumulative Preferred And Preference Stocks [Line Items]
Number of shares authorized	2,000,000
Par value of shares | $ / shares	$ 50
Cumulative Preference Without Par Value [Member] | NIPSCO [Member]
Authorized Classes Of Cumulative Preferred And Preference Stocks [Line Items]
Number of shares authorized	3,000,000
Par value of shares | $ / shares	$ 0

Common Stock (Details)

Common Stock (Details) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Common stock, shares authorized	400,000,000	400,000,000
Common stock, par value	$ 0.01	$ 0.01
Common Stock, Dividends, Per Share, Cash Paid	$ 0.830	$ 1.02	$ 0.98
Dividend Declared	$ 0.155
Dividends Payable, Date to be Paid	Feb. 19, 2016
Dividends Payable, Date of Record	Feb. 8, 2016

Share-Based Compensation (Narra

Share-Based Compensation (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	May. 11, 2010
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock available for awards, shares				8,000,000
Common stock reserved for future awards, shares	5,704,139
Stock-based employee compensation expense	$ 18.8	$ 29.8	$ 19.6
Related tax benefits	7.2	11.8	7.8
Unrecognized compensation cost related to nonvested awards	$ 14.9
Weighted-average remaining requisite service period, years	1 year 8 months
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term	1 year 2 months
401(k) match, profit sharing and non-elective expense	$ 27.4	$ 28.1	$ 21.6
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay	3.00%
Performance Shares Converted to Restricted Stock Unites as a result of the Separation	(2,190,129)
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted	0	535,037	664,776
Fair value of shares granted		$ 16.6	$ 15.7
Shares nonvested	0	1,727,855
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted	660,230	158,633	69,651
Fair value of shares granted	$ 23.9	$ 5.2	$ 1.8
Shares vesting period, (years)	3 years
Shares nonvested	3,142,473	307,329
Performance Shares Converted to Restricted Stock Unites as a result of the Separation	2,190,129
Omnibus Plan [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Units issued	198,996
Director Plan [Member] | Non-Employee Director Award [Domain]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares nonvested	50,092
2014 Award [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares nonvested	808,928
2013 Award [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares nonvested	46,810
2012 Award [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares nonvested	83,415

Share-Based Compensation (Sched

Share-Based Compensation (Schedule Of Transactions Of Restricted Stock Unit) (Details) - $ / shares		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance Shares Converted to Restricted Stock Unites as a result of the Separation		(2,190,129)
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Nonvested, Other Than Options		307,329
Nonvested, Weighted Average Grant Date Fair Value	[1]	$ 27.92
Granted, Other Than Options		660,230	158,633	69,651
Granted, Weighted Average Grant Date Fair Value	[1]	$ 36.23
Forfeited, Other Than Options		(22,860)
Forfeited, Weighted Average Grant Date Fair Value	[1]	$ 16.98
Vested, Other Than Options		(94,380)
Vested, Weighted Average Grant Date Fair Value	[1]	$ 20.61
Nonvested, Other Than Options		3,142,473	307,329
Nonvested, Weighted Average Grant Date Fair Value	[1]	$ 8.55	$ 27.92
Share Based Compensation Arrangement by Share Based Payment Award, Equity Instruments Other Than Options Awards Surrendered due to Separation		(445,123)
Share Based Compensation Arrangement by Share Based Payment Award, Equity Instruments Other Than Options Awards Granted due to Separation		547,148
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number before Valuation Adjustment		952,344
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number before Valuation Adjustment, Weighted Average Grant Date Fair Value	[1]	$ 14.38
Performance Shares Converted to Restricted Stock Unites as a result of the Separation		2,190,129
Performance Shares Converted to Restricted Stock Unites as a result of the Separation, Weighted Average Grant Date Fair Value	[1]	$ 6.01
[1]	The reduction in weighted average grant date fair value during 2015 primarily resulted from the significant number of incremental units issued as a result of the Separation. As discussed above in "Separation-related Adjustments," these incremental units were issued to preserve the intrinsic value of such awards immediately before the Separation.

Share-Based Compensation (Sch94

Share-Based Compensation (Schedule Of Transactions Of Contingent Awards) (Details) - $ / shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance Shares Converted to Restricted Stock Unites as a result of the Separation	(2,190,129)
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Nonvested, Other Than Options	1,727,855
Nonvested, Weighted Average Grant Date Fair Value	$ 24.80
Granted, Other Than Options	0	535,037	664,776
Granted, Weighted Average Grant Date Fair Value	$ 0
Forfeited, Other Than Options	(110,013)
Forfeited, Weighted Average Grant Date Fair Value	$ 9.24
Vested, Other Than Options	(649,896)
Vested, Weighted Average Grant Date Fair Value	$ 20.29
Nonvested, Other Than Options	0	1,727,855
Nonvested, Weighted Average Grant Date Fair Value	$ 6.01	$ 24.80
Share Based Compensation Arrangement by Share Based Payment Award, Equity Instruments Other Than Options Awards Surrendered due to Separation	(573,486)
Share Based Compensation Arrangement by Share Based Payment Award, Equity Instruments Other Than Options Awards Granted due to Separation	1,795,669
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number before Valuation Adjustment	2,190,129
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number before Valuation Adjustment, Weighted Average Grant Date Fair Value	$ 6.01

Long-Term Debt (Narrative) (Det

Long-Term Debt (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Jun. 30, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 04, 2015	Dec. 03, 2015	Nov. 28, 2015	May. 22, 2015	May. 18, 2015	Aug. 20, 2014	Jul. 15, 2014
Debt Instrument [Line Items]
Debt Instrument, Convertible, Conversion Ratio		64
Loss on early extinguishment of long-term debt		$ (97.2)	$ 0	$ 0
Assets		17,492.5	$ 24,589.8
Notional value of interest rate swap											$ 500
Cross default provision on default relating to any indebtedness		50
Security interest and other subset of asset		$ 150
Asset sale covenant percentage of consolidated total assets		10.00%
Percentage of additional subset of assets capped		10.00%
NiSource Finance [Member]
Debt Instrument [Line Items]
Debt Instrument Tendered	$ 750
Extinguishment of Debt, Amount	$ 1,075
Loss on early extinguishment of long-term debt		$ (97.2)
Notional Amount of Fixed Floating Interest Rate Swaps Total		1,000
Notional value of interest rate swap					$ 500	$ 500
NiSource Finance [Member] | 4.45% Notes Due 2021 [Member]
Debt Instrument [Line Items]
Interest rate on debt									4.45%
debt instrument year wise maturity date	2,021
NiSource Finance [Member] | Libor Plus 100 Basis Points Three Year Bank Term Loan Due August 18 2017 [Member]
Debt Instrument [Line Items]
Face amount of notes										$ 750
NiSource Finance [Member] | Long Term Unsecured Notes Due Two Thousand Fifteen [Member]
Debt Instrument [Line Items]
Interest rate on debt							5.36%				5.40%
Debt Instrument, Repurchase Amount							$ 230				$ 500
NiSource Finance [Member] | 5.25% Notes Due 2017 [Member]
Debt Instrument [Line Items]
Interest rate on debt									5.25%
debt instrument year wise maturity date	2,017
NiSource Finance [Member] | 6.40% Notes Due 2018 [Member]
Debt Instrument [Line Items]
Interest rate on debt									6.40%
debt instrument year wise maturity date	2,018
Columbia Pipeline Group [Member]
Debt Instrument [Line Items]
Face amount of notes								$ 2,750
NiSource Excluding NIPSCO [Member]
Debt Instrument [Line Items]
Assets		10,400
NiSource Capital Markets Inc [Member]
Debt Instrument [Line Items]
Face amount of notes		109
Maximum [Member]
Debt Instrument [Line Items]
Cross default provision on default relating to any indebtedness		50
Minimum [Member]
Debt Instrument [Line Items]
Cross default provision on default relating to any indebtedness		$ 5
Revolving Credit Facility [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Convertible, Conversion Ratio		70
Private Placement [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Convertible, Conversion Ratio		75

Long-Term Debt (Schedule Of Out

Long-Term Debt (Schedule Of Outstanding Long Term Debt Sinking Fund Requirements And Maturities) (Details) $ in Millions	Dec. 31, 2015USD ($)
Debt Instrument [Line Items]
2,015	$ 433.7
2,016	362.2
2,017	488.9
2,018	554.7
2,019	563.8
After	4,024.4
Total long-term debt	6,427.7	[1]
Unamortized discount and premium	$ 45.5
[1]	This amount excludes $45.5 million of unamortized discount, premium and expenses.

Short-Term Borrowings (Narrativ

Short-Term Borrowings (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Short-term Debt [Line Items]
Commercial paper outstanding	$ 321.4	$ 792.6
Line of Credit Facility, Amount Outstanding	$ 0	500
Revolving credit facility, termination date	Jul. 1, 2020
Accounts receivable securitization facility borrowings	$ 246	284.3
Letters Of Credit [Member]
Short-term Debt [Line Items]
Letters of Credit Outstanding, Amount	14.7	30.9
Commercial Paper [Member]
Short-term Debt [Line Items]
Revolving credit facility, maximum	1,500
Commercial paper outstanding	321.4
Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Revolving credit facility, maximum	1,500
Standby Letters of Credit [Member]
Short-term Debt [Line Items]
Line of Credit Facility, Amount Outstanding	$ 14.7	$ 14.7

Short-Term Borrowings (Schedule

Short-Term Borrowings (Schedule Of Short-Term Borrowings) (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Short-term Debt [Line Items]
Commercial paper	$ 321.4	$ 792.6
Credit facilities borrowings	0	500
Accounts receivable securitization facility borrowings	246	284.3
Total short-term borrowings	567.4	$ 1,576.9
Commercial Paper [Member]
Short-term Debt [Line Items]
Commercial paper	$ 321.4
Commercial Paper/credit facilities borrowings, weighted average interest rate	1.00%	0.82%
Credit Facilities [Member]
Short-term Debt [Line Items]
Commercial Paper/credit facilities borrowings, weighted average interest rate	0.00%	1.44%
Standby Letters of Credit [Member]
Short-term Debt [Line Items]
Credit facilities borrowings	$ 14.7	$ 14.7

Fair Value (Narrative) (Details

Fair Value (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 04, 2015	Dec. 03, 2015	Jul. 15, 2014
Fair Value Disclosure [Line Items]
Transfers between Fair Value Hierarchies	0
Notional value of interest rate swap						$ 500
Government [Member]
Fair Value Disclosure [Line Items]
Net realized gain on available for sale debt securities	$ 0.2	$ 0.1	$ 0.5
Available-for-sale securities, maturities of less than a year	2.2
Corporate/Other Bonds [Member]
Fair Value Disclosure [Line Items]
Net realized gain on available for sale debt securities	0.2	$ 0.4	$ 0.4
Available-for-sale securities, maturities of less than a year	$ 6.2
NiSource Finance [Member]
Fair Value Disclosure [Line Items]
Notional value of interest rate swap				$ 500	$ 500

Fair Value (Fair Value Of Finan

Fair Value (Fair Value Of Financial Assets And Liabilities Measured On A Recurring Basis) (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available-for-sale securities	$ 128.7	$ 131.9
Fair value assets measured on recurring basis, total	128.8	132
Fair value liabilities measured on recurring basis, total	31.9	14.3
Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available-for-sale securities	0	28.4
Fair value assets measured on recurring basis, total	0.1	28.5
Fair value liabilities measured on recurring basis, total	14.3	14.2
Significant Other Observable Inputs (Level 2) [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available-for-sale securities	128.7	103.5
Fair value assets measured on recurring basis, total	128.7	103.5
Fair value liabilities measured on recurring basis, total	17.4	0
Significant Unobservable Inputs (Level 3) [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Available-for-sale securities	0	0
Fair value assets measured on recurring basis, total	0	0
Fair value liabilities measured on recurring basis, total	0.2	0.1
Commodity Contract [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fair value assets measured on recurring basis, derivative financial instruments	0.1	0.1
Fair value liabilities measured on recurring basis, derivative financial instruments	14.5	14.3
Commodity Contract [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fair value assets measured on recurring basis, derivative financial instruments	0.1	0.1
Fair value liabilities measured on recurring basis, derivative financial instruments	14.3	14.2
Commodity Contract [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fair value assets measured on recurring basis, derivative financial instruments	0	0
Fair value liabilities measured on recurring basis, derivative financial instruments	0	0
Commodity Contract [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fair value assets measured on recurring basis, derivative financial instruments	0	0
Fair value liabilities measured on recurring basis, derivative financial instruments	0.2	$ 0.1
Interest Rate Risk [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fair value liabilities measured on recurring basis, derivative financial instruments	17.4
Interest Rate Risk [Member] | Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fair value liabilities measured on recurring basis, derivative financial instruments	0
Interest Rate Risk [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fair value liabilities measured on recurring basis, derivative financial instruments	17.4
Interest Rate Risk [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fair value liabilities measured on recurring basis, derivative financial instruments	$ 0

Fair Value (Available-For-Sale

Fair Value (Available-For-Sale Debt Securities) (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Fair Value Disclosure [Line Items]
Amortized Cost	$ 129.4	$ 131.4
Gross Unrealized Gains	0.4	1.3
Gross Unrealized Losses	(1.1)	(0.8)
Available-for-sale Securities	128.7	131.9
Government [Member]
Fair Value Disclosure [Line Items]
Amortized Cost	33.7	30.8
Gross Unrealized Gains	0.1	0.3
Gross Unrealized Losses	(0.3)	(0.2)
Available-for-sale Securities	33.5	30.9
Corporate/Other Bonds [Member]
Fair Value Disclosure [Line Items]
Amortized Cost	95.7	100.6
Gross Unrealized Gains	0.3	1
Gross Unrealized Losses	(0.8)	(0.6)
Available-for-sale Securities	$ 95.2	$ 101

Fair Value (Carrying Amount And

Fair Value (Carrying Amount And Estimated Fair Values Of Financial Instruments) (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt (including current portion), Carrying Amount	$ 6,382.2	$ 8,418.1
Long-term debt (including current portion), Estimated Fair Value	$ 6,975.7	$ 9,505.7

Transfers Of Financial Asset103

Transfers Of Financial Assets (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Accounts receivable securitization facility borrowings	$ 246	$ 284.3
Net receivables transferred	246	284.3
Cash from financing activities	38.3	19.2
Securitization transaction fees	2.5	$ 2.9	$ 2.7
Accounts Receivable Program [Member] | Maximum [Member]
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Accounts receivable securitization facility borrowings	515
Columbia Gas Of Ohio Receivables Corporation [Member]
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Net receivables transferred	99.4
Columbia Gas Of Ohio Receivables Corporation [Member] | Maximum [Member]
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Trade receivables, seasonal program maximum	240
NIPSCO Accounts Receivable Corporation [Member]
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Net receivables transferred	111.6
NIPSCO Accounts Receivable Corporation [Member] | Maximum [Member]
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Trade receivables, seasonal program maximum	200
Columbia Gas Of Pennsylvania Receivables Corporation [Member]
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Net receivables transferred	35
Columbia Gas Of Pennsylvania Receivables Corporation [Member] | Maximum [Member]
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Trade receivables, seasonal program maximum	$ 75

Transfers Of Financial Asset104

Transfers Of Financial Assets (Schedule Of Gross And Net Receivables Transferred As Well As Short-Term Borrowings Related To The Securitization Transactions) (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Gross Receivables interest	$ 450.8	$ 611.7
Less: Receivables not transferred	204.8	327.4
Net receivables transferred	246	284.3
Accounts receivable securitization agreements outstanding	$ 246	$ 284.3

Other Commitments And Contin105

Other Commitments And Contingencies (Narrative) (Details) $ in Millions		Apr. 17, 2015USD ($)	Aug. 15, 2014USD ($)	Jul. 31, 2008MW	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)
Other Commitments And Contingencies [Line Items]
Estimated Cost of Compliance with Coal Combustion Residuals, Minimum		$ 100
Estimated Cost of Compliance with Coal Combustion Residuals, Maximum		$ 220
Operating Leases, 2015					$ 18.4
Transmission Upgrade Agreement Multiplier					1.71
Termination date of credit facility					Jul. 1, 2020
Credit facilities borrowings					$ 0	$ 500
Commercial paper					321.4	792.6
Accounts receivable securitization agreements outstanding					246	284.3
Recorded reserves to cover environmental remediation at various sites					123.2	126.6
Payments made in connection with operating leases					47.5	59.8	$ 47.2
Capital lease payments					236.2	286.8
Capital leases related accumulated depreciation					44	86
Pipeline business software annual payment					$ 23.5
Annual capital lease payments number of years					10 years
Capital Leases, Future Minimum Payments, Interest Included in Payments					$ 114.7
Wind power purchase agreement capacity | MW				100
Each wind power purchase agreement capacity | MW				50
Operating Leases, Future Minimum Payments, Due in Two Years					11.1
Operating Leases, 2017					8.8
Operating Leases, 2018					7
Operating Leases, 2019					3.5
Operating Leases, After					$ 13.3
Estimated Cost of Compliance with Clean Water Act, minimum			$ 4
Estimated Cost of Compliance with Clean Water Act, maximum			$ 35
MGP Sites
Other Commitments And Contingencies [Line Items]
Number of waste disposal sites identified by program					64
Liability for estimated remediation costs					$ 110.4	121.5
Reasonably possible remediation costs variance from reserve					25
NIPSCO [Member]
Other Commitments And Contingencies [Line Items]
Capital Lease Obligations					45.5	$ 52.8
Letters Of Credit [Member]
Other Commitments And Contingencies [Line Items]
Guarantees					$ 14.7
Maximum [Member]
Other Commitments And Contingencies [Line Items]
Long term purchase commitment time period					20 years
Maximum [Member] | NIPSCO [Member]
Other Commitments And Contingencies [Line Items]
Payments for capital improvements					$ 860
Remaining Payments for Capital Improvements					$ 28.8
Minimum [Member]
Other Commitments And Contingencies [Line Items]
Long term purchase commitment time period					15 years
Revolving Credit Facility [Member]
Other Commitments And Contingencies [Line Items]
Revolving credit facility, maximum					$ 1,500
Commercial Paper [Member]
Other Commitments And Contingencies [Line Items]
Revolving credit facility, maximum					1,500
Commercial paper					$ 321.4
Pipeline Capacity Transportation And Storage [Member] | Maximum [Member]
Other Commitments And Contingencies [Line Items]
Long term purchase commitment expiration year					2,045
Pipeline Capacity Transportation And Storage [Member] | Minimum [Member]
Other Commitments And Contingencies [Line Items]
Long term purchase commitment expiration year					2,016
IBM Service Agreement [Member]
Other Commitments And Contingencies [Line Items]
Expected Service Fees					$ 410.1
Coal Transportation [Member] | Maximum [Member]
Other Commitments And Contingencies [Line Items]
Long term purchase commitment expiration year					2,018
Fleet Lease [Member]
Other Commitments And Contingencies [Line Items]
Operating Leases, 2015	[1]				$ 30.5
Operating Leases, Future Minimum Payments, Due in Two Years	[1]				30.9
Operating Leases, 2017	[1]				26.7
Operating Leases, 2018	[1]				20.3
Operating Leases, 2019	[1]				12.5
Operating Leases, After	[1]				$ 7.5
[1]	Operating lease balances do not include amounts for fleet leases that can be renewed beyond the initial lease term. The Company anticipates renewing the leases beyond the initial term, but the anticipated payments associated with the renewals do not meet the definition of expected minimum lease payments and therefore are not included above. Expected payments are $30.5 million in 2016, $30.9 million in 2017, $26.7 million in 2018, $20.3 million in 2019, $12.5 million in 2020 and $7.5 million thereafter.

Other Commitments And Contin106

Other Commitments And Contingencies (Existence And Expiration Of Commercial Commitments) (Details) $ in Millions	Dec. 31, 2015USD ($)
Letters Of Credit [Member]
Other Commitments And Contingencies [Line Items]
Total	$ 14.7

Other Commitments And Contin107

Other Commitments And Contingencies (Future Minimum Lease Payments Required Under Operating And Capital Leases) (Details) $ in Millions	Dec. 31, 2015USD ($)
Unrecorded Unconditional Purchase Obligation [Line Items]
Operating Leases, 2015	$ 18.4
Operating Leases, 2016	11.1
Operating Leases, 2017	8.8
Operating Leases, 2018	7
Operating Leases, 2019	3.5
Operating Leases, After	13.3
Operating Leases, Total future minimum payments	62.1
Capital Leases, 2015	23.5
Capital Leases, 2016	23
Capital Leases, 2017	23.3
Capital Leases, 2018	23.7
Capital Leases, 2019	23.5
Capital Leases, After	196.3
Capital Leases, Total future minimum payments	313.3
Capital Leases, Future Minimum Payments, Interest Included in Payments	114.7
Fleet Lease [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Operating Leases, 2015	30.5	[1]
Operating Leases, 2016	30.9	[1]
Operating Leases, 2017	26.7	[1]
Operating Leases, 2018	20.3	[1]
Operating Leases, 2019	12.5	[1]
Operating Leases, After	$ 7.5	[1]
[1]	Operating lease balances do not include amounts for fleet leases that can be renewed beyond the initial lease term. The Company anticipates renewing the leases beyond the initial term, but the anticipated payments associated with the renewals do not meet the definition of expected minimum lease payments and therefore are not included above. Expected payments are $30.5 million in 2016, $30.9 million in 2017, $26.7 million in 2018, $20.3 million in 2019, $12.5 million in 2020 and $7.5 million thereafter.

Other Commitments And Contin108

Other Commitments And Contingencies (Estimated Aggregate Amounts Of Minimum Fixed Payments On Purchase And Service Obligations) (Details) $ in Millions	Dec. 31, 2015USD ($)
Other Commitments And Contingencies [Line Items]
Purchase And Service Obligations Minimum Fixed Payments Due Current	$ 844.9
2,015	720.8
2,016	508.3
2,018	399.2
2,019	291.9
After	430.3
Total purchase and service obligations	3,195.4
Energy Commodity Agreements [Member]
Other Commitments And Contingencies [Line Items]
Purchase And Service Obligations Minimum Fixed Payments Due Current	169.3
2,015	74.8
2,016	67.5
2,018	70.6
2,019	72.6
After	0.4
Total purchase and service obligations	455.2
Pipeline Service Agreements [Member]
Other Commitments And Contingencies [Line Items]
Purchase And Service Obligations Minimum Fixed Payments Due Current	512.7
2,015	496
2,016	341
2,018	245.4
2,019	139.3
After	429.9
Total purchase and service obligations	2,164.3
IBM Service Agreement [Member]
Other Commitments And Contingencies [Line Items]
Purchase And Service Obligations Minimum Fixed Payments Due Current	90.9
2,015	82.8
2,016	80.1
2,018	78.6
2,019	77.7
After	0
Expected Service Fees	410.1
Other Service Agreements [Member]
Other Commitments And Contingencies [Line Items]
Purchase And Service Obligations Minimum Fixed Payments Due Current	72
2,015	67.2
2,016	19.7
2,018	4.6
2,019	2.3
After	0
Total purchase and service obligations	$ 165.8

Accumulated Other Comprehens109

Accumulated Other Comprehensive Loss (Narrative) (Details)	12 Months Ended
	Dec. 31, 2015
Millennium Pipeline Company, L.L.C [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Unrealized loss, amortization period	15 years

Accumulated Other Comprehens110

Accumulated Other Comprehensive Loss (Components Of Accumulated Other Comprehensive Loss) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax		$ (16.5)	$ (9.6)	$ 15.5
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		5.5	2.6	6.4
Other Comprehensive Income (Loss), Net of Tax		(11)	(7)	21.9
Allocation of AOCI to Noncontrolling Interest	[1]	2
Distribution of Spinoff		24.5
Accumulated other comprehensive loss		(35.1)	(50.6)	(43.6)	$ (65.5)
Accumulated Net Unrealized Investment Gain (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax		(0.5)	0.9	(2.4)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		(0.3)	(0.3)	(0.5)
Other Comprehensive Income (Loss), Net of Tax		(0.8)	0.6	(2.9)
Allocation of AOCI to Noncontrolling Interest		0
Distribution of Spinoff		0
Accumulated other comprehensive loss		(0.5)	0.3	(0.3)	2.6
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax		(11)	(0.3)	0.1
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		3.2	2.5	2.7
Other Comprehensive Income (Loss), Net of Tax		(7.8)	2.2	2.8
Allocation of AOCI to Noncontrolling Interest		2
Distribution of Spinoff		13.9
Accumulated other comprehensive loss		(15.5)	(23.6)	(25.8)	(28.6)
Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax		(5)	(10.2)	17.8
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		2.6	0.4	4.2
Other Comprehensive Income (Loss), Net of Tax		(2.4)	(9.8)	22
Allocation of AOCI to Noncontrolling Interest		0
Distribution of Spinoff		10.6
Accumulated other comprehensive loss		$ (19.1)	$ (27.3)	$ (17.5)	$ (39.5)
[1]	This transaction, which occurred prior to the Separation, was distributed through retained earnings as part of the Separation on July 1, 2015.

Other, Net (Schedule Of Other N

Other, Net (Schedule Of Other Net) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Other Nonoperating Income (Expense) [Abstract]
Interest income		$ 0.8	$ 3.8	$ 3.5
AFUDC Equity		11.5	10.7	11.7
Charitable Contributions		(4.8)	(11.1)	(8.2)
Miscellaneous Non-Operating Income (Expense)	[1]	9.9	10	(0.2)
Total Other, net		$ 17.4	$ 13.4	$ 6.8
[1]	Miscellaneous primarily consists of transmission upgrade agreement income in 2015 and 2014.

Interest Expense, Net (Details)

Interest Expense, Net (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Interest Expense [Abstract]
Interest on long-term debt		$ 377.5	$ 368.6	$ 364.4
Interest on short-term borrowings	[1]	2.2	5.2	2.7
Debt discount/cost amortization		8.7	8	7.5
Accounts receivable securitization		2.5	2.9	2.7
Allowance for borrowed funds used and interest capitalized during construction		(5.4)	(5.3)	(6.1)
Other		(5.3)	0.1	4.1
Total Interest Expense, net		$ 380.2	$ 379.5	$ 375.3
[1]	Refer to Note 15, "Short-Term Borrowings," for additional information.

Segments Of Business (Narrative

Segments Of Business (Narrative) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)
Segment Reporting Information [Line Items]
Number of Reportable Segments	2
Number of counties in which electric service provided by Electric Operations	20
Revenues	$ 4,651.8	$ 5,272.4	$ 4,625.4

Segments Of Business (Schedule

Segments Of Business (Schedule Of Operating Income Derived From Revenues And Expenses By Segment) (Details) - USD ($) $ in Millions		3 Months Ended									12 Months Ended
		Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014		Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014		Dec. 31, 2013
Segment Reporting Information [Line Items]
Unaffiliated											$ 4,651.8	$ 5,272.4		$ 4,625.4
Operating Income		$ 219.5	$ 109.7	$ 84.4	$ 386.3	$ 226.9		$ 71.1	$ 117.8	$ 373.3	799.9	789.1		698.1
Consolidated Depreciation and Amortization											524.4	486.9		470.4
Consolidated Assets		17,492.5				24,589.8					17,492.5	24,589.8
Payments to Acquire Property Plant and Equipment Including Captial Expenditures From Current Liabilities And Equity Method Investments	[1]										1,367.5	1,339.6		1,248.5
Gas Distribution Operations [Member]
Segment Reporting Information [Line Items]
Unaffiliated											3,069.1	3,593.9		3,053.8
Operating Income											555.8	537		445.4
Consolidated Depreciation and Amortization											232.6	217.6		201.4
Consolidated Assets		10,094.5				9,443.7					10,094.5	9,443.7
Payments to Acquire Property Plant and Equipment Including Captial Expenditures From Current Liabilities And Equity Method Investments	[1]										917	860.3		790.8
Electric Operations [Member]
Segment Reporting Information [Line Items]
Unaffiliated											1,574.4	1,673.4		1,564.9
Operating Income											264.4	282.7		265.5
Consolidated Depreciation and Amortization											267.7	244.4		244.4
Consolidated Assets		5,265.3				5,009.9					5,265.3	5,009.9
Payments to Acquire Property Plant and Equipment Including Captial Expenditures From Current Liabilities And Equity Method Investments	[1]										400.3	438.8		426.3
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Unaffiliated											405.9	418.7		377.9
Operating Income											(20.3)	(30.6)		(12.8)
Consolidated Depreciation and Amortization											24.1	24.9		24.6
Consolidated Assets		$ 2,132.7				$ 10,136.2	[2]				2,132.7	10,136.2	[2]
Payments to Acquire Property Plant and Equipment Including Captial Expenditures From Current Liabilities And Equity Method Investments	[1]										50.2	40.5		31.4
Eliminations [Member]
Segment Reporting Information [Line Items]
Unaffiliated											(397.6)	(413.6)		(371.2)
Unaffiliated [Member] | Gas Distribution Operations [Member]
Segment Reporting Information [Line Items]
Unaffiliated											3,068.7	3,593.6		3,053.5
Unaffiliated [Member] | Electric Operations [Member]
Segment Reporting Information [Line Items]
Unaffiliated											1,573.6	1,672.6		1,564.2
Unaffiliated [Member] | Corporate and Other [Member]
Segment Reporting Information [Line Items]
Unaffiliated											9.5	6.2		7.7
Intersegment [Member] | Gas Distribution Operations [Member]
Segment Reporting Information [Line Items]
Unaffiliated											0.4	0.3		0.3
Intersegment [Member] | Electric Operations [Member]
Segment Reporting Information [Line Items]
Unaffiliated											0.8	0.8		0.7
Intersegment [Member] | Corporate and Other [Member]
Segment Reporting Information [Line Items]
Unaffiliated											$ 396.4	$ 412.5		$ 370.2
[1]	Amounts differ from those presented on the Statements of Consolidated Cash Flows primarily due to the inclusion of capital expenditures included in current liabilities and AFUDC Equity.
[2]	The 2014 balances for Corporate and Other includes assets of Discontinued Operations refer to Note 3 "Discontinued Operations," for additional information.

Quarterly Financial Data (Narra

Quarterly Financial Data (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Quarterly Financial Data [Line Items]
Gain (Loss) on Disposition of Discontinued Operations - net of taxes	$ 0	$ 0	$ 34.9

Quarterly Financial Data (Sched

Quarterly Financial Data (Schedule Of Quarterly Financial Data) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended																12 Months Ended
	Dec. 31, 2015		Sep. 30, 2015		Jun. 30, 2015		Mar. 31, 2015		Dec. 31, 2014		Sep. 30, 2014		Jun. 30, 2014		Mar. 31, 2014		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Quarterly Financial Data [Line Items]
Gross Revenues	$ 1,097.8		$ 817.2		$ 884.6		$ 1,852.2		$ 1,393.3		$ 838.2		$ 1,023.7		$ 2,017.2		$ 4,651.8	$ 5,272.4	$ 4,625.4
Operating Income	219.5		109.7		84.4		386.3		226.9		71.1		117.8		373.3		799.9	789.1	698.1
Income from Continuing Operations	64.4		14.8		(73.1)		192.5		79.5		(17.2)		20.8		173.1		198.6	256.2	221
Results from Discontinued Operations-net of taxes	(5)	[1]	(19.7)	[1]	45.4	[1]	82.8	[1]	74.7	[1]	48.6	[1]	57.4	[1]	93.1	[1]	87.9	273.8	311.1
Net Income	$ 59.4		$ (4.9)		(36.4)		268.4		$ 154.2		$ 31.4		$ 78.2		$ 266.2		286.5	530	532.1
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest					$ (27.7)		$ 275.3										$ 302.1	$ 530	$ 532.1
Basic Earnings (Loss) Per Share, Continuing Operations	$ 0.20		$ 0.05		$ (0.23)		$ 0.61		$ 0.25		$ (0.05)		$ 0.07		$ 0.55		$ 0.63	$ 0.81	$ 0.71
Basic Earnings (Loss) Per Share, Discontinued Operations	(0.01)		(0.07)		0.12		0.24		0.24		0.15		0.18		0.30		0.27	0.87	0.99
Basic Earnings (Loss) Per Share	0.19		(0.02)		(0.11)		0.85		0.49		0.10		0.25		0.85		0.90	1.68	1.70
Diluted Earnings (Loss) Per Share, Continuing Operations	0.20		0.05		(0.23)		0.61		0.25		(0.05)		0.07		0.55		0.63	0.81	0.71
Diluted Earnings (Loss) Per Share, Discontinued Operations	(0.01)		(0.07)		0.12		0.24		0.24		0.15		0.18		0.30		0.27	0.86	0.99
Diluted Earnings (Loss) Per Share	$ 0.19		$ (0.02)		$ (0.11)		$ 0.85		$ 0.49		$ 0.10		$ 0.25		$ 0.85		$ 0.90	$ 1.67	$ 1.70
[1]	Includes the results of the former Columbia Pipeline Group segment.

Quarterly Financial Data Schedu

Quarterly Financial Data Schedule of Previously Disclosed Results (Details) - USD ($) $ in Millions	3 Months Ended																12 Months Ended
	Dec. 31, 2015		Sep. 30, 2015		Jun. 30, 2015		Mar. 31, 2015		Dec. 31, 2014		Sep. 30, 2014		Jun. 30, 2014		Mar. 31, 2014		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Quarterly Financial Data [Line Items]
Revenue, Net	$ 1,097.8		$ 817.2		$ 884.6		$ 1,852.2		$ 1,393.3		$ 838.2		$ 1,023.7		$ 2,017.2		$ 4,651.8	$ 5,272.4	$ 4,625.4
Operating Income	219.5		109.7		84.4		386.3		226.9		71.1		117.8		373.3		799.9	789.1	698.1
Income from continuing operations	64.4		14.8		(73.1)		192.5		79.5		(17.2)		20.8		173.1		198.6	256.2	221
Income from Discontinued Operations - net of taxes	$ (5)	[1]	$ (19.7)	[1]	45.4	[1]	82.8	[1]	$ 74.7	[1]	48.6	[1]	57.4	[1]	93.1	[1]	$ 87.9	273.8	$ 311.1
Scenario, Previously Reported [Member]
Quarterly Financial Data [Line Items]
Revenue, Net					1,169		2,149.7				1,123.9		1,335.1		2,320.5			1,691.1
Operating Income					165.1		530.1				157.8		219.6		533.7			351.3
Income from continuing operations					(27.4)		275.3				31.5		78.5		266.4			154.3
Income from Discontinued Operations - net of taxes					$ (0.3)		$ 0				$ (0.1)		$ (0.3)		$ (0.2)			$ (0.1)
[1]	Includes the results of the former Columbia Pipeline Group segment.

Supplemental Cash Flow Infor118

Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Supplemental Cash Flow [Line Items]
Capital expenditures included in current liabilities	$ 121.6	$ 127.4	$ 96.7
Assets acquired under a capital lease	47.5	76.7	28.4
Interest Paid, Net	390.4	429.3	402.7
Cash paid for income taxes	$ 21.3	$ 19.4	$ 10.4

Valuation And Qualifying Acc119

Valuation And Qualifying Accounts (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Reserve For Accounts Receivable [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning Balance		$ 24.9	$ 23.4	$ 23.8
Valuation Allowances and Reserves, Charged to Cost and Expense		22.5	21.8	13.8
Valuation Allowances and Reserves, Charged to Other Accounts	[1]	56.7	69.9	55.3
Deductions for Purposes for which Reserves were Created		83.8	90.2	69.5
Ending Balance		20.3	24.9	23.4
Reserve For Other Investments [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning Balance		3	3	3
Valuation Allowances and Reserves, Charged to Cost and Expense		0	0	0
Valuation Allowances and Reserves, Charged to Other Accounts	[1]	0	0	0
Deductions for Purposes for which Reserves were Created		0	0	0
Ending Balance		$ 3	$ 3	$ 3
[1]	Charged to Other Accounts reflects the deferral of bad debt expense to a regulatory asset.