Fair Value Disclosures (Net Gains (Losses) Due to Changes in Fair Value for Items Measured at Fair Value Pursuant to the Fair Value Option Election) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Early adoption effect
Fair Value Option Quantitative Disclosures
Unrealized gain recognized in OCI	$ 323
Securities purchased under agreements to resell
Fair Value Option Quantitative Disclosures
Gains (losses) due to changes in fair value	2	$ (1)
Deposits
Fair Value Option Quantitative Disclosures
Gains (losses) due to changes in fair value	(2)
Short-term borrowings
Fair Value Option Quantitative Disclosures
Gains (losses) due to changes in fair value	45	(40)
Securities Sold under agreements to repurchase
Fair Value Option Quantitative Disclosures
Gains (losses) due to changes in fair value	(11)	(3)
Long-term borrowings
Fair Value Option Quantitative Disclosures
Gains (losses) due to changes in fair value	(1,104)	805
Trading \| Securities purchased under agreements to resell
Fair Value Option Quantitative Disclosures
Gains (losses) due to changes in fair value	0	(1)
Trading \| Deposits
Fair Value Option Quantitative Disclosures
Gains (losses) due to changes in fair value	(2)
Trading \| Short-term borrowings
Fair Value Option Quantitative Disclosures
Gains (losses) due to changes in fair value	45	(40)
Trading \| Securities Sold under agreements to repurchase
Fair Value Option Quantitative Disclosures
Gains (losses) due to changes in fair value	(9)	(2)
Trading \| Long-term borrowings
Fair Value Option Quantitative Disclosures
Gains (losses) due to changes in fair value	(965)	937
Interest Income (Expense) \| Securities purchased under agreements to resell
Fair Value Option Quantitative Disclosures
Gains (losses) due to changes in fair value	2	0
Interest Income (Expense) \| Deposits
Fair Value Option Quantitative Disclosures
Gains (losses) due to changes in fair value	0
Interest Income (Expense) \| Short-term borrowings
Fair Value Option Quantitative Disclosures
Gains (losses) due to changes in fair value	0	0
Interest Income (Expense) \| Securities Sold under agreements to repurchase
Fair Value Option Quantitative Disclosures
Gains (losses) due to changes in fair value	(2)	(1)
Interest Income (Expense) \| Long-term borrowings
Fair Value Option Quantitative Disclosures
Gains (losses) due to changes in fair value	$ (139)	$ (132)