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) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($)	Jan. 01, 2019 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Number of loan portfolio segments	4
Operating lease, right-of-use assets	$ 168
Operating lease, liabilities	$ 196
Phase-in of capital impact of Accounting Standards Update 2016-13	25.00%
Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease, right-of-use assets		$ 161
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	$ 29
Operating lease, liabilities		$ 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
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Phase-in of capital impact of Accounting Standards Update 2016-13	25.00%
Accounting Standards Update 2016-13 | Accumulated Deficit
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	$ (1,000)
Accounting Standards Update 2016-13 | Allowance for loan losses
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	$ (1,300)