Description of Business, Basis of Presentation, and Changes in Significant Accounting Policies Description of Business, Basis of Presentation, and Changes in Significant Accounting Policies (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2019	Jan. 01, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating Lease, Right-of-Use Asset	$ 168
Operating Lease, Liability	195
Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating Lease, Right-of-Use Asset		$ 161
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	29
Operating Lease, Liability		$ 190
Accounting Standards Update 2017-08 | Accumulated Deficit
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	10
Accounting Standards Update 2017-08 | Accumulated other comprehensive (loss) income
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	$ (8)
Accounting Standards Update 2016-13 | Minimum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for Loan Losses, Estimated Increase (Decrease), Percent	105.00%
Accounting Standards Update 2016-13 | Maximum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Allowance for Loan Losses, Estimated Increase (Decrease), Percent	115.00%