Income Taxes - Schedule of Significant Components of Deferred Income Tax Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2024	Mar. 31, 2024	Dec. 31, 2023		Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022
Assets
Other Employee Benefit Plans	$ 104		$ 103
Other	464		459
Total	568		562
Liabilities
Accelerated Depreciation	7,651		7,621
Other	642		640
Total	8,293		8,261
Net Deferred Income Tax Liabilities	$ 7,725	$ 7,708	$ 7,699	[1]	$ 7,637	$ 7,605	$ 7,552	$ 7,520

[1] See Note 20, Revision of Prior Period Financial Statements.