Stockholders' Equity and EPS - Common Stock (Details) - USD ($) $ / shares in Units, $ in Millions	Aug. 12, 2021	Jul. 01, 2021	Apr. 14, 2021	Mar. 22, 2021	Sep. 30, 2021	Dec. 31, 2020
Class of Stock [Line Items]
Common stock, shares, issued					58,677,483	51,888,463
Boston Private
Class of Stock [Line Items]
Number of shares of SIVB common stock that each share of Boston Private common stock was converted		0.0228
Common Stock
Class of Stock [Line Items]
Common stock, shares, issued	2,227,000		300,000	2,000,000
Shares issued, price per share	$ 564.00			$ 500.00
Net proceeds after deducting discounts and commissions	$ 1,200		$ 146	$ 972
Common Stock | Boston Private
Class of Stock [Line Items]
Issuance of common stock for the acquisition of Boston Private (in shares)		1,887,981
Number of shares of SIVB common stock that each share of Boston Private common stock was converted		0.0228