Regulatory Matters (Tables)

12 Months Ended

Dec. 31, 2016

Regulatory Capital Requirements [Abstract]

Summary Of Actual Capital Amounts And Ratios For The Company And Its Three Largest Subsidiary Banks

	December 31, 2016				To be well-capitalized
(In thousands)	Amount		Ratio		Amount		Ratio
Transitional Basis Basel III Regulatory Capital Rules
Total capital (to risk-weighted assets)
The Company	$	7,608,502	15.24	%	$	4,993,671	10.00	%
ZB, National Association	7,277,987		14.61		4,983,000		10.00
Tier 1 capital (to risk-weighted assets)
The Company	6,737,638		13.49		3,994,937		8.00
ZB, National Association	6,654,990		13.36		3,986,400		8.00
Common equity tier 1 capital (Basel III)
The Company	6,028,037		12.07		3,245,886		6.50
ZB, National Association	5,824,090		11.69		3,238,950		6.50
Tier 1 capital (to average assets)
The Company	6,737,638		11.09		na		na 1
ZB, National Association	6,654,990		10.99		3,027,427		5.00

	December 31, 2015				To be well-capitalized
(In thousands)	Amount		Ratio		Amount		Ratio
Transitional Basis Basel III Regulatory Capital Rules
Total capital (to risk-weighted assets)
The Company	$	7,535,760	16.12	%	$	4,674,725	10.00	%
ZB, National Association	6,918,312		14.84		4,661,581		10.00
Tier 1 capital (to risk-weighted assets)
The Company	6,580,326		14.08		3,739,780		8.00
ZB, National Association	6,334,391		13.59		3,729,265		8.00
Common equity tier 1 capital (Basel III)
The Company	5,711,836		12.22		3,038,571		6.50
ZB, National Association	5,503,491		11.81		3,030,028		6.50
Tier 1 capital (to average assets)
The Company	6,580,326		11.26		na		na 1
ZB, National Association	6,334,391		10.97		2,886,732		5.00

¹  There is no Tier 1 leverage ratio component in the definition of a well-capitalized bank holding company.