Basis of Presentation - Narrative (Details) - USD ($)	Jan. 01, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase in assets		$ 1,823,000,000
Increase in liabilities		2,121,000,000
Decrease in shareholders' equity		66,558,000,000	$ 30,178,000,000	$ 29,695,000,000	$ 29,926,000,000
Estimated Impact of Lease Accounting Standard
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase in assets		860,000,000
Increase in liabilities		997,000,000
Decrease in shareholders' equity		$ 31,000,000
Estimated CECL impact on Allowance for Credit Losses | Subsequent Event
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Decrease in shareholders' equity	$ 2,100,000,000
financing receivable, allowance for credit loss, period increase percent	$ 2,900,000,000