Regulatory Matters - GAS Nicor Gas (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended		12 Months Ended
	Sep. 30, 2023	Jun. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2019
Public Utilities, General Disclosures [Line Items]
Total operating revenues	$ (6,980)		$ (8,378)	$ (19,208)	$ (22,232)
Total operating expenses	4,870		$ 6,185	$ 14,589	$ 17,000
Nicor Gas
Public Utilities, General Disclosures [Line Items]
Pre-tax charge to income	38
After-tax charge to income	$ 28
Nicor Gas | Investing in Illinois
Public Utilities, General Disclosures [Line Items]
Capital expenditures disallowed						$ 32
Capital expenditures						$ 415
Total operating revenues		$ 8
Total operating expenses		$ 30