Loans and Allowance for Credit Losses, Loans by Credit Quality Indicator, Commercial (Details) - USD ($) $ in Millions		Jun. 30, 2017	Dec. 31, 2016	Dec. 31, 2008
Loans and Leases Receivable Disclosure [Abstract]
Loans	[1]	$ 957,423	$ 967,604
Total Commercial [Member]
Loans and Leases Receivable Disclosure [Abstract]
Loans		505,901	506,536
Commercial and Industrial Loans [Member]
Loans and Leases Receivable Disclosure [Abstract]
Loans		331,113	330,840
Commercial real estate mortgage [Member]
Loans and Leases Receivable Disclosure [Abstract]
Loans		130,277	132,491
Commercial Real Estate Construction [Member]
Loans and Leases Receivable Disclosure [Abstract]
Loans		25,337	23,916
Commercial Lease Financing Receivable [Member]
Loans and Leases Receivable Disclosure [Abstract]
Loans		19,174	19,289
Loans Excluding Purchased Credit-Impaired Loans [Member]
Loans and Leases Receivable Disclosure [Abstract]
Financing Receivable, Recorded Investment, Nonaccrual Status		9,056	10,384
Loans Excluding Purchased Credit-Impaired Loans [Member] | Commercial Real Estate Mortgage and Construction Loans [Member] | Criticized [Member]
Loans and Leases Receivable Disclosure [Abstract]
Loans		5,200
Financing Receivable, Recorded Investment, Nonaccrual Status		664
Loans Excluding Purchased Credit-Impaired Loans [Member] | Total Commercial [Member]
Loans and Leases Receivable Disclosure [Abstract]
Loans		505,638	505,859
Financing Receivable, Recorded Investment, Nonaccrual Status		3,385	4,059
Loans Excluding Purchased Credit-Impaired Loans [Member] | Total Commercial [Member] | Pass [Member]
Loans and Leases Receivable Disclosure [Abstract]
Loans		480,229	476,266
Loans Excluding Purchased Credit-Impaired Loans [Member] | Total Commercial [Member] | Criticized [Member]
Loans and Leases Receivable Disclosure [Abstract]
Loans		25,409	29,593
Loans Excluding Purchased Credit-Impaired Loans [Member] | Commercial and Industrial Loans [Member]
Loans and Leases Receivable Disclosure [Abstract]
Loans		330,982	330,603
Financing Receivable, Recorded Investment, Nonaccrual Status		2,632	3,216
Loans Excluding Purchased Credit-Impaired Loans [Member] | Commercial and Industrial Loans [Member] | Pass [Member]
Loans and Leases Receivable Disclosure [Abstract]
Loans		311,963	308,166
Loans Excluding Purchased Credit-Impaired Loans [Member] | Commercial and Industrial Loans [Member] | Criticized [Member]
Loans and Leases Receivable Disclosure [Abstract]
Loans		19,019	22,437
Loans Excluding Purchased Credit-Impaired Loans [Member] | Commercial real estate mortgage [Member]
Loans and Leases Receivable Disclosure [Abstract]
Loans		130,158	132,108
Financing Receivable, Recorded Investment, Nonaccrual Status		630	685
Loans Excluding Purchased Credit-Impaired Loans [Member] | Commercial real estate mortgage [Member] | Pass [Member]
Loans and Leases Receivable Disclosure [Abstract]
Loans		125,283	126,793
Loans Excluding Purchased Credit-Impaired Loans [Member] | Commercial real estate mortgage [Member] | Criticized [Member]
Loans and Leases Receivable Disclosure [Abstract]
Loans		4,875	5,315
Loans Excluding Purchased Credit-Impaired Loans [Member] | Commercial Real Estate Construction [Member]
Loans and Leases Receivable Disclosure [Abstract]
Loans		25,324	23,859
Financing Receivable, Recorded Investment, Nonaccrual Status		34	43
Loans Excluding Purchased Credit-Impaired Loans [Member] | Commercial Real Estate Construction [Member] | Pass [Member]
Loans and Leases Receivable Disclosure [Abstract]
Loans		25,013	23,408
Loans Excluding Purchased Credit-Impaired Loans [Member] | Commercial Real Estate Construction [Member] | Criticized [Member]
Loans and Leases Receivable Disclosure [Abstract]
Loans		311	451
Loans Excluding Purchased Credit-Impaired Loans [Member] | Commercial Lease Financing Receivable [Member]
Loans and Leases Receivable Disclosure [Abstract]
Loans		19,174	19,289
Financing Receivable, Recorded Investment, Nonaccrual Status		89	115
Loans Excluding Purchased Credit-Impaired Loans [Member] | Commercial Lease Financing Receivable [Member] | Pass [Member]
Loans and Leases Receivable Disclosure [Abstract]
Loans		17,970	17,899
Loans Excluding Purchased Credit-Impaired Loans [Member] | Commercial Lease Financing Receivable [Member] | Criticized [Member]
Loans and Leases Receivable Disclosure [Abstract]
Loans		1,204	1,390
PCI Loans Carrying Value [Member]
Loans and Leases Receivable Disclosure [Abstract]
PCI loans		14,273	16,731
PCI Loans Carrying Value [Member] | Total Commercial [Member]
Loans and Leases Receivable Disclosure [Abstract]
PCI loans		263	677	$ 18,700
PCI Loans Carrying Value [Member] | Commercial and Industrial Loans [Member]
Loans and Leases Receivable Disclosure [Abstract]
PCI loans		131	237
PCI Loans Carrying Value [Member] | Commercial real estate mortgage [Member]
Loans and Leases Receivable Disclosure [Abstract]
PCI loans		119	383
PCI Loans Carrying Value [Member] | Commercial Real Estate Construction [Member]
Loans and Leases Receivable Disclosure [Abstract]
PCI loans		13	57
PCI Loans Carrying Value [Member] | Commercial Lease Financing Receivable [Member]
Loans and Leases Receivable Disclosure [Abstract]
PCI loans		$ 0	$ 0

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