Goodwill represents the excess of the cost of an acquisition over the fair value of the identifiable net assets acquired. The table below shows our goodwill balances by segment at June 30, 2024. We had no changes to the carrying amount of goodwill during the six months ended June 30, 2024.


(in millions)	Wisconsin		Illinois		Other States		Non-Utility Energy Infrastructure		Total
Goodwill balance (1)	$	2,104.3	$	758.7	$	183.2	$	6.6	$	3,052.8

At both June 30, 2024 and December 31, 2023, we had $29.3 million of indefinite-lived intangible assets, largely consisting of spectrum frequencies. The spectrum frequencies enable the utilities to transmit data and voice communications over a wavelength dedicated to us throughout our service territories. We also have $5.2 million of other indefinite-lived intangible assets, consisting of a MGU trade name from a previous acquisition. These indefinite-lived intangible assets are included in other long-term assets on our balance sheets.


	June 30, 2024						December 31, 2023
(in millions)	Gross Carrying Amount		Accumulated Amortization		Net Carrying Amount		Gross Carrying Amount		Accumulated Amortization		Net Carrying Amount
PPAs (1)	$	653.9	$	(93.0)	$	560.9	$	653.9	$	(66.6)	$	587.3
Proxy revenue swap (2)	7.2		(3.8)		3.4		7.2		(3.5)		3.7
Interconnection agreements (3)	4.7		(1.0)		3.7		4.7		(0.9)		3.8
Total intangible liabilities	$	665.8	$	(97.8)	$	568.0	$	665.8	$	(71.0)	$	594.8

(1) Represents PPAs related to the acquisition of Blooming Grove, Tatanka Ridge, Jayhawk, Thunderhead Wind Energy LLC, Samson I, and Sapphire Sky expiring between 2030 and 2037. The weighted-average remaining useful life of the PPAs is 11 years.

(2) Represents an agreement with a counterparty to swap the market revenue of Upstream Wind Energy LLC's wind generation for fixed quarterly payments over 10 years, which expires in February 2029. The remaining useful life of the proxy revenue swap is five years.

(3) Represents interconnection agreements related to the acquisitions of Tatanka Ridge and Bishop Hill Energy III LLC, expiring in 2040 and 2041, respectively. These agreements relate to payments for connecting our facilities to the infrastructure of another utility to facilitate the movement of power onto the electric grid. The weighted-average remaining useful life of the interconnection agreements is 16 years.

Amortization related to these intangible liabilities for the three and six months ended June 30, 2024, was $13.4 million and $26.8 million, respectively. Amortization for the three and six months ended June 30, 2023, was $13.4 million and $23.8 million, respectively. Amortization for the next five years, including amounts recorded through June 30, 2024, is estimated to be:


	For the Years Ending December 31
(in millions)	2024		2025		2026		2027		2028
Amortization to be recorded as an increase to operating revenues	$	53.4	$	53.4	$	53.4	$	53.4	$	53.4
Amortization to be recorded as a decrease to other operation and maintenance	0.2		0.2		0.2		0.2		0.2