Variable Interest Entities - Multi-seller conduits (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018
Variable Interest Entity [Line Items]
Unfunded lending-related commitments	$ 1,060,801	$ 1,039,258	$ 1,022,023
Multi-seller conduits
Variable Interest Entity [Line Items]
Commercial paper eliminated in consolidation	12,600	20,100
Multi-seller conduits | Commercial and other
Variable Interest Entity [Line Items]
Unfunded lending-related commitments	$ 8,700	$ 8,000