Loans and Related Allowance for Credit Losses, Allowance for Credit Losses (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Jan. 01, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable, allowance for credit loss, period increase (decrease)	$ 2,900
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Provision for credit losses, loans	3,833	$ 845
Interest income on certain loans	(38)	(39)
Loan charge-offs	(1,238)	(1,063)
Loan recoveries	329	368
Net loan charge-offs	(909)	(695)
Other	9	3
Allowance for credit losses for loans, ending balance	12,022	10,821
Components:
Allowance for loan losses			$ 11,263		$ 9,551
Allowance for credit losses, loans	$ 12,022	$ 10,821	$ 12,022		10,456	$ 10,821
Net loan charge-offs (annualized) as a percentage of average total loans	0.38%	0.30%
Allowance for loan losses as a percentage of total loans			1.12%			1.04%
Allowance for credit losses for loans as a percentage of total loans			1.19%			1.14%
Purchase credit deteriorated [Member]
Components:
Allowance for credit losses, loans					0
Previous accounting guidance [Member]
Components:
Allowance for credit losses, loans					10,456		$ 10,707
Accounting Standards Update 2016-13 [Member] | Cumulative effect from change in accounting policies, period of adoption adjustment [Member] | Not purchased credit deteriorated [Member]
Components:
Allowance for credit losses, loans					(1,337)		0
Accounting Standards Update 2016-13 [Member] | Cumulative effect from change in accounting policies, period of adoption adjustment [Member] | Purchase credit deteriorated [Member]
Components:
Allowance for credit losses, loans					8		0
Accounting Standards Update 2016-13 [Member] | Cumulative effect from change in accounting policies, period of adoption adjusted balance [Member]
Components:
Allowance for credit losses, loans					9,127		10,707
Allowance for loan losses [Member]
Components:
Allowance for loan losses			$ 11,263			$ 9,900
Allowance for unfunded credit commitments [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for credit losses for loans, ending balance	$ 759	$ 921
Components:
Allowance for credit losses, loans	759	921	759			921
Total Commercial [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Provision for credit losses, loans	2,240	164
Interest income on certain loans	(14)	(11)
Loan charge-offs	(393)	(200)
Loan recoveries	69	55
Net loan charge-offs	(324)	(145)
Other	(7)	3
Allowance for credit losses for loans, ending balance	5,279	6,428
Components:
Allowance for credit losses, loans	5,279	6,428	5,279		6,245	6,428
Total Commercial [Member] | Purchase credit deteriorated [Member]
Components:
Allowance for credit losses, loans					0
Total Commercial [Member] | Previous accounting guidance [Member]
Components:
Allowance for credit losses, loans					6,245		6,417
Total Commercial [Member] | Accounting Standards Update 2016-13 [Member] | Cumulative effect from change in accounting policies, period of adoption adjustment [Member]
Components:
Allowance for credit losses, loans				$ (2,900)
Total Commercial [Member] | Accounting Standards Update 2016-13 [Member] | Cumulative effect from change in accounting policies, period of adoption adjustment [Member] | Not purchased credit deteriorated [Member]
Components:
Allowance for credit losses, loans					(2,861)		0
Total Commercial [Member] | Accounting Standards Update 2016-13 [Member] | Cumulative effect from change in accounting policies, period of adoption adjustment [Member] | Purchase credit deteriorated [Member]
Components:
Allowance for credit losses, loans					0		0
Total Commercial [Member] | Accounting Standards Update 2016-13 [Member] | Cumulative effect from change in accounting policies, period of adoption adjusted balance [Member]
Components:
Allowance for credit losses, loans				3,400	3,384		6,417
Commercial and industrial loans [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Loan charge-offs	(377)	(176)
Loan recoveries	44	43
Commercial real estate mortgage [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Loan charge-offs	(3)	(12)
Loan recoveries	5	6
Commercial real estate construction [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Loan charge-offs	0	(1)
Loan recoveries	16	3
Commercial lease financing receivable [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Loan charge-offs	(13)	(11)
Loan recoveries	4	3
Total Consumer [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Provision for credit losses, loans	1,593	681
Interest income on certain loans	(24)	(28)
Loan charge-offs	(845)	(863)
Loan recoveries	260	313
Net loan charge-offs	(585)	(550)
Other	16	0
Allowance for credit losses for loans, ending balance	6,743	4,393
Components:
Allowance for credit losses, loans	6,743	4,393	$ 6,743		4,211	$ 4,393
Total Consumer [Member] | Purchase credit deteriorated [Member]
Components:
Allowance for credit losses, loans					0
Total Consumer [Member] | Previous accounting guidance [Member]
Components:
Allowance for credit losses, loans					4,211		4,290
Total Consumer [Member] | Accounting Standards Update 2016-13 [Member] | Cumulative effect from change in accounting policies, period of adoption adjustment [Member]
Components:
Allowance for credit losses, loans				1,500
Total Consumer [Member] | Accounting Standards Update 2016-13 [Member] | Cumulative effect from change in accounting policies, period of adoption adjustment [Member] | Not purchased credit deteriorated [Member]
Components:
Allowance for credit losses, loans					1,524		0
Total Consumer [Member] | Accounting Standards Update 2016-13 [Member] | Cumulative effect from change in accounting policies, period of adoption adjustment [Member] | Purchase credit deteriorated [Member]
Components:
Allowance for credit losses, loans					8		0
Total Consumer [Member] | Accounting Standards Update 2016-13 [Member] | Cumulative effect from change in accounting policies, period of adoption adjusted balance [Member]
Components:
Allowance for credit losses, loans				5,700	5,743		$ 4,290
Real estate 1-4 family first mortgage [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Loan charge-offs	(23)	(43)
Loan recoveries	26	55
Real estate 1-4 family junior lien mortgage [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Loan charge-offs	(30)	(34)
Loan recoveries	35	43
Credit card [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Loan charge-offs	(471)	(437)
Loan recoveries	94	85
Credit card [Member] | Previous accounting guidance [Member]
Components:
Allowance for credit losses, loans					2,300
Credit card [Member] | Accounting Standards Update 2016-13 [Member] | Cumulative effect from change in accounting policies, period of adoption adjustment [Member]
Components:
Allowance for credit losses, loans				700
Credit card [Member] | Accounting Standards Update 2016-13 [Member] | Cumulative effect from change in accounting policies, period of adoption adjusted balance [Member]
Components:
Allowance for credit losses, loans				2,900
Automobile [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Loan charge-offs	(156)	(187)
Loan recoveries	74	96
Automobile [Member] | Previous accounting guidance [Member]
Components:
Allowance for credit losses, loans					500
Automobile [Member] | Accounting Standards Update 2016-13 [Member] | Cumulative effect from change in accounting policies, period of adoption adjustment [Member]
Components:
Allowance for credit losses, loans				300
Automobile [Member] | Accounting Standards Update 2016-13 [Member] | Cumulative effect from change in accounting policies, period of adoption adjusted balance [Member]
Components:
Allowance for credit losses, loans				700
Other revolving credit and installment [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Loan charge-offs	(165)	(162)
Loan recoveries	$ 31	$ 34
Other revolving credit and installment [Member] | Previous accounting guidance [Member]
Components:
Allowance for credit losses, loans					$ 600
Other revolving credit and installment [Member] | Accounting Standards Update 2016-13 [Member] | Cumulative effect from change in accounting policies, period of adoption adjustment [Member]
Components:
Allowance for credit losses, loans				600
Other revolving credit and installment [Member] | Accounting Standards Update 2016-13 [Member] | Cumulative effect from change in accounting policies, period of adoption adjusted balance [Member]
Components:
Allowance for credit losses, loans				$ 1,200