Commitments and Contingencies (Remediation Cost Estimates) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Loss Contingencies [Line Items]
Total remediation costs—undiscounted	$ 188	$ 193
Weighted-average discount rate	5.10%	5.10%
Total remediation costs—discounted	$ 124	$ 128
Recoverable portion	$ 81	$ 82