Derivative Instruments and Hedging Activities (Gains (Losses) on Accounting Hedges and Trading Revenues by Product Type) (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Trading Revenues by Product Type
Trading revenues	$ 3,770	$ 3,235
Borrowings
ASU 2017-12 Derivatives and Hedging-Targeted Improvements to Accounting for Hedging Activities
Carrying amount of Borrowings currently or previously hedged	107,264
Interest Rate Contracts
Trading Revenues by Product Type
Trading revenues	871	594
Foreign Exchange Contracts
Trading Revenues by Product Type
Trading revenues	261	235
Equity Security and Index Contracts
Trading Revenues by Product Type
Trading revenues	1,877	1,641
Commodity and Other Contracts
Trading Revenues by Product Type
Trading revenues	435	189
Credit Contracts
Trading Revenues by Product Type
Trading revenues	326	576
Fair Value Hedges \| Interest Expense \| Interest Rate Contracts
Gain (Loss) on Fair Value Hedges Recognized in Interest Expense
Gains (losses) recognized in Interest Expense	(1,841)	(805)
Fair Value Hedges \| Interest Expense \| Borrowings
Gain (Loss) on Fair Value Hedges Recognized in Interest Expense
Gains (losses) recognized in Interest Expense	1,852	717
Outstanding Hedges \| Borrowings
ASU 2017-12 Derivatives and Hedging-Targeted Improvements to Accounting for Hedging Activities
Basis adjustments included in carrying amount	2,035
Net Investment Hedges \| Foreign Exchange Contracts
Net Investment Hedges
Gains (losses) recognized in OCI	(148)	(205)
Forward points excluded from hedge effectiveness testing - Interest income	$ 7	$ (9)

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Amount of liability hedged in fair value hedging relationship.

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Amount of cumulative increase (decrease) in carrying value of hedged liability in fair value hedge, attributable to hedged risk.

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The portion of gains and losses (net) on derivative instruments designated and qualifying as hedging instruments representing (a) the amount of the hedge ineffectiveness and (b) the amount, if any, excluded from the assessment of hedge effectiveness.

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The effective portion of gains and losses (net) on derivative instruments designated and qualifying as hedging instruments that was recognized in other comprehensive income during the current period.

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Aggregate net gain and losses (whether realized or unrealized) on all derivative instruments held for trading purposes whether or not settled physically.

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Total amount of gain (loss) derived from fair value hedges recognized in earnings in the period.

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Amount of gain (loss) resulting from the difference between the acquisition price and the selling price or fair value of trading assets and trading liabilities, conducted separately from customer trading activities. Includes, but is not limited to, changes in fair value of trading assets and trading liabilities.

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