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		3 Months Ended
	Jan. 01, 2020	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Equity	$ (13,399)	$ (13,519)	$ (13,699)	$ (14,416)	$ (13,266)	$ (13,268)
Allowance for Loan and Lease Losses, Adjustments, Other		$ (1)	1
Phase-in of capital impact of Accounting Standards Update 2016-13		25.00%
CECL scaling factor		25.00%
Accounting Standards Update 2016-13
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Equity	1,017
Allowance for Loan and Lease Losses, Adjustments, Other	1,300
Phase-in of capital impact of Accounting Standards Update 2016-13		25.00%
CECL scaling factor		25.00%
Accumulated Deficit
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Equity	5,074	$ 5,465	$ 5,195	$ 4,057	$ 5,499	$ 5,489
Accumulated Deficit | Accounting Standards Update 2016-13
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Equity	$ 1,017