Fair Value Disclosures (Gains (Losses) Due to Changes in Instrument-Specific Credit Risk) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Fair Value disclosure
Cumulative pre-tax DVA gain (loss) recognized in AOCI	$ (1,236)		$ (1,831)
Loans and Other Debt | OCI
Fair Value disclosure
Gains (losses) due to changes in instrument-specific credit risk	0	$ 0
Loans and Other Debt | Trading Revenues
Fair Value disclosure
Gains (losses) due to changes in instrument-specific credit risk	81	(3)
Lending Commitments | OCI
Fair Value disclosure
Gains (losses) due to changes in instrument-specific credit risk	0	0
Lending Commitments | Trading Revenues
Fair Value disclosure
Gains (losses) due to changes in instrument-specific credit risk	2	0
Securities Sold Under Agreements to Repurchase | OCI
Fair Value disclosure
Gains (losses) due to changes in instrument-specific credit risk	2	(3)
Securities Sold Under Agreements to Repurchase | Trading Revenues
Fair Value disclosure
Gains (losses) due to changes in instrument-specific credit risk	0	0
Borrowings | OCI
Fair Value disclosure
Gains (losses) due to changes in instrument-specific credit risk	593	14
Borrowings | Trading Revenues
Fair Value disclosure
Gains (losses) due to changes in instrument-specific credit risk	$ (15)	$ (4)