Long-Term Borrowings - Unsecured Long-Term Borrowings (Detail) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Fixed-rate obligations	$ 132,642	$ 136,589
Floating-rate obligations	84,236	87,560
Total	216,878	224,149
U.S. Dollar [Member]
Debt Instrument [Line Items]
Fixed-rate obligations	96,921	99,935
Floating-rate obligations	52,452	54,321
Total	149,373	154,256
Non-U.S. Dollar [Member]
Debt Instrument [Line Items]
Fixed-rate obligations	35,721	36,654
Floating-rate obligations	31,784	33,239
Total	$ 67,505	$ 69,893