Parent Company Financial Statements - Consolidated Balance Sheet of Parent Company Only (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	$ 1,383	$ 599
Other assets	1,193	1,102
Total Assets	37,354	34,615	$ 33,102
Other liabilities	374	390
Long-term borrowings	1,095	1,340
Long-term	81	90
Total Liabilities	32,395	29,732
Stockholders' equity attributable to parent	4,959	4,883	$ 4,608	$ 4,409
Total Liabilities and Stockholders’ Equity	37,354	34,615
Parent Company
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	380	251
Other assets	10	18
Total Assets	5,825	5,445
Other liabilities	40	34
Advances from affiliates	197	197
Long-term borrowings	621	323
Short-term	7	7
Long-term	1	1
Total Liabilities	866	562
Stockholders' equity attributable to parent	4,959	4,883
Total Liabilities and Stockholders’ Equity	5,825	5,445
Parent Company | Bank Subsidiary
Condensed Balance Sheet Statements, Captions [Line Items]
Investment in and advances to subsidiaries	5,064	5,072
Parent Company | Non-bank Subsidiaries
Condensed Balance Sheet Statements, Captions [Line Items]
Investment in and advances to subsidiaries	$ 371	$ 104