Consolidated Statements of Capitalization $ in Millions	12 Months Ended
Dec. 31, 2018 USD ($) number_of_interest_rate_swaps	Dec. 31, 2017 USD ($)
Preferred stock of subsidiary	$ 30.4	$ 30.4
Obligations under capital leases	23.3	27.0
Total	10,410.9	9,627.9
Integrys acquisition fair value adjustment	20.6	26.9
Unamortized debt issuance costs	(44.7)	(38.0)
Unamortized discount, net and other	(27.8)	(28.1)
Total long-term debt, including current portion	10,359.0	9,588.7
Current portion of long-term debt and capital lease obligations	(365.0)	(842.1)
Total long-term debt	9,994.0	8,746.6
Total long-term capitalization	$ 19,813.3	18,238.4
Number of interest rate swaps executed \| number_of_interest_rate_swaps	2
WE \| WE Debentures (unsecured), 1.70% due 2018
Interest rate, (as a percent)	1.70%
Long-Term debt, Unsecured	$ 0.0	250.0
WE \| WE Debentures (unsecured), 4.25% due 2019
Interest rate, (as a percent)	4.25%
Long-Term debt, Unsecured	$ 250.0	250.0
WE \| WE Debentures (unsecured), 2.95% due 2021
Interest rate, (as a percent)	2.95%
Long-Term debt, Unsecured	$ 300.0	300.0
WE \| WE Debentures (unsecured), 3.10% due 2025
Interest rate, (as a percent)	3.10%
Long-Term debt, Unsecured	$ 250.0	250.0
WE \| WE Debentures (unsecured), 6.50% due 2028
Interest rate, (as a percent)	6.50%
Long-Term debt, Unsecured	$ 150.0	150.0
WE \| WE Debentures (unsecured), 5.625% due 2033
Interest rate, (as a percent)	5.625%
Long-Term debt, Unsecured	$ 335.0	335.0
WE \| WE Debentures (unsecured), 5.70% due 2036
Interest rate, (as a percent)	5.70%
Long-Term debt, Unsecured	$ 300.0	300.0
WE \| WE Debentures (unsecured), 3.65% due 2042
Interest rate, (as a percent)	3.65%
Long-Term debt, Unsecured	$ 250.0	250.0
WE \| WE Debentures (unsecured), 4.25% due 2044
Interest rate, (as a percent)	4.25%
Long-Term debt, Unsecured	$ 250.0	250.0
WE \| WE Debentures (unsecured), 4.30% due 2045
Interest rate, (as a percent)	4.30%
Long-Term debt, Unsecured	$ 250.0	250.0
WE \| WE Debentures (unsecured), 4.30% due 2048
Interest rate, (as a percent)	4.30%
Long-Term debt, Unsecured	$ 300.0	0.0
WE \| WE Debentures (unsecured), 6.875% due 2095
Interest rate, (as a percent)	6.875%
Long-Term debt, Unsecured	$ 100.0	100.0
WPS \| WPS Senior Notes (unsecured), 1.65% due 2018
Interest rate, (as a percent)	1.65%
Long-Term debt, Unsecured	$ 0.0	250.0
WPS \| WPS Senior Notes (unsecured), 3.35% due 2021
Interest rate, (as a percent)	3.35%
Long-Term debt, Unsecured	$ 400.0	0.0
WPS \| WPS Senior Notes (unsecured), 6.08% due 2028
Interest rate, (as a percent)	6.08%
Long-Term debt, Unsecured	$ 50.0	50.0
WPS \| WPS Senior Notes (unsecured), 5.55% due 2036
Interest rate, (as a percent)	5.55%
Long-Term debt, Unsecured	$ 125.0	125.0
WPS \| WPS Senior Notes (unsecured), 3.671% due 2042
Interest rate, (as a percent)	3.671%
Long-Term debt, Unsecured	$ 300.0	300.0
WPS \| WPS Senior Notes (unsecured), 4.752% due 2044
Interest rate, (as a percent)	4.752%
Long-Term debt, Unsecured	$ 450.0	450.0
WG \| WG Debentures (unsecured), 3.53% due 2025
Interest rate, (as a percent)	3.53%
Long-Term debt, Unsecured	$ 200.0	200.0
WG \| WG Debentures (unsecured), 5.90% due 2035
Interest rate, (as a percent)	5.90%
Long-Term debt, Unsecured	$ 90.0	90.0
WG \| WG Debentures (unsecured), 3.71% due 2046
Interest rate, (as a percent)	3.71%
Long-Term debt, Unsecured	$ 200.0	200.0
PGL \| PGL First and Refunding Mortgage Bonds (secured), 8.00% due 2018
Interest rate, (as a percent)	8.00%
Long-Term debt, Secured	$ 0.0	5.0
PGL \| PGL First and Refunding Mortgage Bonds (secured), 4.63% due 2019
Interest rate, (as a percent)	4.63%
Long-Term debt, Secured	$ 75.0	75.0
PGL \| PGL First and Refunding Mortgage Bonds (secured), 3.87% due 2028
Interest rate, (as a percent)	3.87%
Long-Term debt, Secured	$ 150.0	0.0
PGL \| PGL First and Refunding Mortgage Bonds (secured), 3.90% due 2030
Interest rate, (as a percent)	3.90%
Long-Term debt, Secured	$ 50.0	50.0
PGL \| PGL First and Refunding Mortgage Bonds (secured), 1.875% due 2033
Interest rate, (as a percent)	1.875%
Long-Term debt, Secured	$ 50.0	50.0
PGL \| PGL First and Refunding Mortgage Bonds (secured), 4.0% due 2033
Interest rate, (as a percent)	4.00%
Long-Term debt, Secured	$ 50.0	50.0
PGL \| PGL First and Refunding Mortgage Bonds (secured), 3.98% due 2042
Interest rate, (as a percent)	3.98%
Long-Term debt, Secured	$ 100.0	100.0
PGL \| PGL First and Refunding Mortgage Bonds (secured), 3.96% due 2043
Interest rate, (as a percent)	3.96%
Long-Term debt, Secured	$ 220.0	220.0
PGL \| PGL First and Refunding Mortgage Bonds (secured), 4.21% due 2044
Interest rate, (as a percent)	4.21%
Long-Term debt, Secured	$ 200.0	200.0
PGL \| PGL First and Refunding Mortgage Bonds (secured), 3.65% due 2046
Interest rate, (as a percent)	3.65%
Long-Term debt, Secured	$ 50.0	50.0
PGL \| PGL First and Refunding Mortgage Bonds (secured), 3.65% due 2046
Interest rate, (as a percent)	3.65%
Long-Term debt, Secured	$ 150.0	150.0
PGL \| PGL First and Refunding Mortgage Bonds (secured), 3.77% due 2047
Interest rate, (as a percent)	3.77%
Long-Term debt, Secured	$ 100.0	100.0
NSG \| NSG First Mortgage Bonds (secured), 3.43% due 2027
Interest rate, (as a percent)	3.43%
Long-Term debt, Secured	$ 28.0	28.0
NSG \| NSG First Mortgage Bonds (secured), 3.87% due 2028
Interest rate, (as a percent)	3.87%
Long-Term debt, Secured	$ 50.0	0.0
NSG \| NSG First Mortgage Bonds (secured), 3.96% due 2043
Interest rate, (as a percent)	3.96%
Long-Term debt, Secured	$ 54.0	54.0
MGU \| MGU Senior Notes (unsecured), 3.11% due 2027
Interest rate, (as a percent)	3.11%
Long-Term debt, Unsecured	$ 30.0	30.0
MGU \| MGU Senior Notes (unsecured), 3.41% due 2032
Interest rate, (as a percent)	3.41%
Long-Term debt, Unsecured	$ 30.0	30.0
MGU \| MGU Senior Notes (unsecured), 4.01% due 2047
Interest rate, (as a percent)	4.01%
Long-Term debt, Unsecured	$ 30.0	30.0
MERC \| MERC Senior Notes (unsecured), 3.11% due 2027
Interest rate, (as a percent)	3.11%
Long-Term debt, Unsecured	$ 40.0	40.0
MERC \| MERC Senior Notes (unsecured), 3.41% due 2032
Interest rate, (as a percent)	3.41%
Long-Term debt, Unsecured	$ 40.0	40.0
MERC \| MERC Senior Notes (unsecured), 4.01% due 2047
Interest rate, (as a percent)	4.01%
Long-Term debt, Unsecured	$ 40.0	40.0
Bluewater Gas Storage, LLC \| Bluewater Gas Storage Senior Notes (unsecured), 3.76% due 2047
Interest rate, (as a percent)	3.76%
Long-Term debt, Unsecured	$ 122.7	125.0
We Power \| We Power Subsidiaries Notes (secured, nonrecourse), 4.91% due 2019-2030
Interest rate, (as a percent)	4.91%
Long-Term debt, Secured	$ 95.1	101.0
We Power \| We Power Subsidiaries Notes (secured, nonrecourse), 5.209% due 2019-2030
Interest rate, (as a percent)	5.209%
Long-Term debt, Secured	$ 182.7	194.1
We Power \| We Power Subsidiaries Notes (secured, nonrecourse), 4.673% due 2019-2031
Interest rate, (as a percent)	4.673%
Long-Term debt, Secured	$ 153.5	162.4
We Power \| We Power Subsidiaries Notes (secured, nonrecourse), 6.00% due 2019-2033
Interest rate, (as a percent)	6.00%
Long-Term debt, Secured	$ 116.6	121.5
We Power \| We Power Subsidiaries Notes (secured, nonrecourse), 6.09% due 2030-2040
Interest rate, (as a percent)	6.09%
Long-Term debt, Secured	$ 275.0	275.0
We Power \| We Power Subsidiaries Notes (secured, nonrecourse), 5.848% due 2031-2041
Interest rate, (as a percent)	5.848%
Long-Term debt, Secured	$ 215.0	215.0
WECC \| WECC Notes (unsecured), 6.94% due 2028
Interest rate, (as a percent)	6.94%
Long-Term debt, Unsecured	$ 50.0	50.0
Integrys Holding Inc \| Integrys Senior Notes (unsecured), 4.17% due 2020
Interest rate, (as a percent)	4.17%
Long-Term debt, Unsecured	$ 250.0	250.0
Integrys Holding Inc \| Integrys Junior Notes (unsecured), 3.60% due 2066
Interest rate, (as a percent)	3.60%
Long-Term debt, Unsecured	$ 0.0	114.9
Integrys Holding Inc \| Integrys Junior Notes (unsecured), 6.00% due 2073
Interest rate, (as a percent)	6.00%
Long-Term debt, Unsecured	$ 400.0	400.0
ATC Holding LLC \| ATC Holding Senior Notes (unsecured), 4.18% due 2025
Interest rate, (as a percent)	4.18%
Long-Term debt, Unsecured	$ 85.0	0.0
ATC Holding LLC \| ATC Holding Senior Notes (unsecured), 4.37% due 2028
Interest rate, (as a percent)	4.37%
Long-Term debt, Unsecured	$ 56.5	0.0
ATC Holding LLC \| ATC Holding 4.47% Senior Notes due December 20, 2030
Interest rate, (as a percent)	4.47%
Long-Term debt, Unsecured	$ 98.5	0.0
WEC Energy Group
Common shareholder's equity	$ 9,788.9	9,461.4
WEC Energy Group \| Interest rate swaps
Number of interest rate swaps executed \| number_of_interest_rate_swaps	2
Interest rate swap fixed interest rate	4.9765%
Interest rate swap notional value	$ 250.0
WEC Energy Group \| WEC Energy Group Senior Notes (unsecured), 1.65%, due 2018
Interest rate, (as a percent)	1.65%
Long-Term debt, Unsecured	$ 0.0	300.0
WEC Energy Group \| WEC Energy Group Senior Notes (unsecured), 2.45% due 2020
Interest rate, (as a percent)	2.45%
Long-Term debt, Unsecured	$ 400.0	400.0
WEC Energy Group \| WEC Energy Group Senior Notes (unsecured), 3.375%, due 2021
Interest rate, (as a percent)	3.375%
Long-Term debt, Unsecured	$ 600.0	0.0
WEC Energy Group \| WEC Energy Group Senior Notes (unsecured), 3.55% due 2025
Interest rate, (as a percent)	3.55%
Long-Term debt, Unsecured	$ 500.0	500.0
WEC Energy Group \| WEC Energy Group Senior Notes (unsecured), 6.20% due 2033
Interest rate, (as a percent)	6.20%
Long-Term debt, Unsecured	$ 200.0	$ 200.0
WEC Energy Group \| WEC Energy Group Junior Notes (unsecured), 3.53% due 2067
Interest rate, (as a percent)	4.73%	3.53%
Weighted average interest rate (as a percent)	4.8533%
Long-Term debt, Unsecured	$ 500.0	$ 500.0
Common shareholder's equity
Common shareholder's equity	9,788.9	9,461.4
Preferred stock of subsidiary
Common shareholder's equity	$ 30.4	$ 30.4

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
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