Income Taxes (Deferred Tax Assets for Loss and Tax Credit Carryforwards) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Income Taxes [Line Items]
Net operating losses	$ 340
Tax credits	48
Deferred Tax Assets Loss And Tax Credit Carry Forward	388	$ 479
Tax Years 2019 Through 2023 [Member]
Income Taxes [Line Items]
Net operating losses	137
Deferred Tax Assets Loss And Tax Credit Carry Forward	137
Tax Years 2024 Through 2028 [Member]
Income Taxes [Line Items]
Net operating losses	30
Tax credits	24
Deferred Tax Assets Loss And Tax Credit Carry Forward	54
Tax Years 2029 Through 2038 [Member]
Income Taxes [Line Items]
Net operating losses	28
Tax credits	19
Deferred Tax Assets Loss And Tax Credit Carry Forward	47
Indefinite [Member]
Income Taxes [Line Items]
Net operating losses	145
Tax credits	5
Deferred Tax Assets Loss And Tax Credit Carry Forward	$ 150