Fair Values - Borrowings Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Fair Value Measurements
Borrowings at fair value	$ 61,654	$ 51,184
Recurring | Equity
Fair Value Measurements
Borrowings at fair value	29,508	24,494
Recurring | Interest Rates
Fair Value Measurements
Borrowings at fair value	26,427	22,343
Recurring | Commodity and other
Fair Value Measurements
Borrowings at fair value	3,973	2,735
Recurring | Credit
Fair Value Measurements
Borrowings at fair value	1,229	856
Recurring | Foreign exchange
Fair Value Measurements
Borrowings at fair value	$ 517	$ 756