Income Taxes - Net Operating Loss Carryforwards (Details) $ in Millions	Dec. 31, 2018 USD ($)
Operating Loss Carryforwards [Line Items]
Total gross carryforwards related to net operating losses	$ 1,828
2019
Operating Loss Carryforwards [Line Items]
Total gross carryforwards related to net operating losses	25
2020
Operating Loss Carryforwards [Line Items]
Total gross carryforwards related to net operating losses	87
2021
Operating Loss Carryforwards [Line Items]
Total gross carryforwards related to net operating losses	81
2022
Operating Loss Carryforwards [Line Items]
Total gross carryforwards related to net operating losses	34
2023
Operating Loss Carryforwards [Line Items]
Total gross carryforwards related to net operating losses	7
2024
Operating Loss Carryforwards [Line Items]
Total gross carryforwards related to net operating losses	7
2025-2045
Operating Loss Carryforwards [Line Items]
Total gross carryforwards related to net operating losses	55
Do not expire
Operating Loss Carryforwards [Line Items]
Total gross carryforwards related to net operating losses	$ 1,532