Income Taxes And Tax-Related Items Reconciliation of Expected Income Tax Expense at the Federal Statutory Rate to the Corporation's Provision for Income Taxes (Details) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Document Period End Date										Dec. 31, 2019
Tax based on federal statutory rate, amount										$ 322	$ 323	$ 432
Tax based on federal statutory rate, percent										21.00%	21.00%	35.00%
State income tax, amount										$ 33	$ 35	$ 22
State income tax, percent										2.20%	2.30%	1.80%
Employee Stock Transactions, amount										$ 12	$ 23	$ 35
Employee Stock Transactions, percent										(0.80%)	(1.50%)	(2.80%)
Capitalization and recovery positions, amount	[1]									$ 0	$ (17)	$ 0
Capitalization and recovery positions, percent	[1]									0.00%	(1.10%)	0.00%
Affordable housing and historic credits, amount										$ (11)	$ (12)	$ (21)
Affordable housing and historic credits, percent										(0.70%)	(0.80%)	(1.70%)
Bank-owned life insurance, amount										$ (9)	$ (9)	$ (16)
Bank-owned life insurance, percent										(0.60%)	(0.60%)	(1.30%)
Remeasurement of the Corporation's deferred tax balance										$ 0	$ 8	$ (107)
Remearsurement of deferred taxes, percent										0.00%	0.50%	(8.70%)
FDIC fees, amount	[2]									$ 5	$ 8	$ 0
FDIC fees, percent	[2]									0.30%	0.50%	0.00%
Other changes in unrecognized tax benefits, amount										$ 0	$ 4	$ 0
Other changes in unrecognized tax benefits, percent										0.00%	0.30%	0.00%
Tax-related interest and penalties, amount										$ 2	$ (3)	$ 4
Tax-related interest and penalties, percent										0.10%	(0.20%)	0.30%
Lease termination transactions, amount										$ 0	$ 0	$ (2)
Lease termination transactions, percent										0.00%	0.00%	(0.20%)
Other, amount										$ 4	$ 2	$ 0
Other, percent										0.20%	0.10%	0.00%
Provision for income taxes, amount		$ 82	$ 80	$ 87	$ 85	$ 90	$ 63	$ 54	$ 93	$ 334	$ 300	$ 491
Provision for income taxes, percent										21.70%	19.50%	39.80%

[1] Tax benefits from the review of tax capitalization and recovery positions related to software and fixed assets included in the 2017 tax return.

[2] Beginning January 1, 2018, FDIC insurance expense is no longer deductible as a result of the enactment of the Tax Cuts and Jobs Act.