Cash and Marketable Securities (Summary Of Amortized Cost Fair Value And Gross Unrealized Gains And Losses Of Marketable Securities By Contractual Maturity) (Details) $ in Millions	Dec. 31, 2024 USD ($)
Amortized Cost
One year or less	$ 15
After one year through five years	16
After five years through ten years	8
After ten years	2
Mortgage-backed securities	12
Total Amortized Cost	53
Fair Value
One year or less	15
After one year through five years	16
After five years through ten years	8
After ten years	2
Mortgage-backed securities	12
Total Fair Value	$ 53