Income Taxes Income Taxes - Operating Loss and Tax Credit Carryforwards (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	$ 442	$ 531
Tax Credit Carryforwards	55	230
Total Operating Loss and Tax Credit Carryforwards	497	761
Expiring within Five Years [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	99	131
Tax Credit Carryforwards	14	30
Expiring After Five Years Or Having Indefinite Expiration [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	343	400
Tax Credit Carryforwards	$ 41	$ 200