Fair Value, Estimates for Financial Instruments Excluding those Recorded at Fair Value on a Recurring Basis (Details) - USD ($) $ in Millions		Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2015
Financial assets
Cash and due from banks		$ 19,206	$ 20,729	$ 19,287	$ 19,111
Federal funds sold, securities purchased under resale agreements and other short-term investments		273,105	266,038
Held-to-maturity securities		142,423	99,583
Loans	[1]	951,873	967,604
Excluding investments at NAV		7,667	8,397
Financial liabilities
Deposits		1,306,706	1,306,079
Short-term borrowings		93,811	96,781
Long-term debt		238,893	255,077
Capital Lease Obligations		39	7
Carrying value [Member]
Financial assets
Cash and due from banks		19,206	20,729
Federal funds sold, securities purchased under resale agreements and other short-term investments		273,105	266,038
Held-to-maturity securities		142,423	99,583
Mortgages held for sale		3,525	4,267
Loans held for sale		157	80
Loans		921,420	936,358
Excluding investments at NAV		7,642	8,362
Investments Net Asset Value		25	35
Financial liabilities
Deposits		1,306,706	1,306,079
Short-term borrowings		93,811	96,781
Long-term debt		238,854	255,070
Financial Liabilities Fair Value Disclosure		1,639,371	1,657,930
Estimated fair value [Member]
Financial assets
Cash and due from banks		19,206	20,729
Federal funds sold, securities purchased under resale agreements and other short-term investments		273,105	266,038
Held-to-maturity securities		142,818	99,155
Mortgages held for sale		3,529	4,277
Loans held for sale		157	81
Loans		935,918	947,834
Excluding investments at NAV		8,107	8,942
Investments Net Asset Value		27	48
Financial liabilities
Deposits		1,306,694	1,306,153
Short-term borrowings		93,811	96,781
Long-term debt		243,152	255,779
Financial Liabilities Fair Value Disclosure		1,643,657	1,658,713
Loan Commitments And Standby, Commercial And Similar Letters of Credit		1,100	1,200
Estimated fair value [Member] | Fair Value, Inputs, Level 1 [Member]
Financial assets
Cash and due from banks		19,206	20,729
Federal funds sold, securities purchased under resale agreements and other short-term investments		206,073	207,003
Held-to-maturity securities		45,282	45,079
Mortgages held for sale		0	0
Loans held for sale		0	0
Loans		0	0
Excluding investments at NAV		0	0
Assets		270,561	272,811
Financial liabilities
Deposits		0	0
Short-term borrowings		0	0
Long-term debt		0	0
Financial Liabilities Fair Value Disclosure		0	0
Estimated fair value [Member] | Fair Value, Inputs, Level 2 [Member]
Financial assets
Cash and due from banks		0	0
Federal funds sold, securities purchased under resale agreements and other short-term investments		66,963	58,953
Held-to-maturity securities		96,627	51,706
Mortgages held for sale		2,189	2,927
Loans held for sale		157	81
Loans		54,106	60,245
Excluding investments at NAV		23	18
Assets		220,065	173,930
Financial liabilities
Deposits		1,285,239	1,282,158
Short-term borrowings		93,811	96,781
Long-term debt		240,846	245,704
Financial Liabilities Fair Value Disclosure		1,619,896	1,624,643
Estimated fair value [Member] | Fair Value, Inputs, Level 3 [Member]
Financial assets
Cash and due from banks		0	0
Federal funds sold, securities purchased under resale agreements and other short-term investments		69	82
Held-to-maturity securities		909	2,370
Mortgages held for sale		1,340	1,350
Loans held for sale		0	0
Loans		881,812	887,589
Excluding investments at NAV		8,084	8,924
Assets		892,214	900,315
Financial liabilities
Deposits		21,455	23,995
Short-term borrowings		0	0
Long-term debt		2,306	10,075
Financial Liabilities Fair Value Disclosure		23,761	34,070
Finance Leases Financing Receivable [Member]
Financial assets
Loans		19,200	19,300
Excluding NAV Investments [Member] | Carrying value [Member]
Financial assets
Assets		1,367,478	1,335,417
Excluding NAV Investments [Member] | Estimated fair value [Member]
Financial assets
Assets		1,382,840	1,347,056
Including NAV Investments [Member] | Carrying value [Member]
Financial assets
Assets		1,367,503	1,335,452
Including NAV Investments [Member] | Estimated fair value [Member]
Financial assets
Assets		$ 1,382,867	$ 1,347,104

[1] Parenthetical amounts represent assets and liabilities for which we have elected the fair value option.