Variable Interest Entities - Multi-seller conduits (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018
Variable Interest Entity [Line Items]
Unfunded lending-related commitments	$ 1,079,762	$ 1,039,258	$ 1,045,993
Multi-seller conduits
Variable Interest Entity [Line Items]
Commercial paper eliminated in consolidation	8,200	20,100
Multi-seller conduits | Commercial and other
Variable Interest Entity [Line Items]
Unfunded lending-related commitments	$ 8,400	$ 8,000