Parent Company Financial Statements - Consolidated Balance Sheet of Parent Company Only (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	$ 599	$ 488
Other assets	1,102	823
Total Assets	34,615	33,102	$ 31,418
Other liabilities	390	283
Long-term borrowings	1,340	627
Long-term	90	87
Total Liabilities	29,732	28,494
Stockholders' Equity	4,883	4,608	$ 4,409	$ 2,572
Total Liabilities and Stockholders’ Equity	34,615	33,102
Parent Company
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	251	254
Other assets	18	19
Total Assets	5,445	5,124
Other liabilities	34	32
Advances from affiliates	197	197
Long-term borrowings	323	279
Short-term	7	7
Long-term	1	1
Total Liabilities	562	516
Stockholders' Equity	4,883	4,608
Total Liabilities and Stockholders’ Equity	5,445	5,124
Parent Company | Bank Subsidiary
Condensed Balance Sheet Statements, Captions [Line Items]
Investment in and advances to subsidiaries	5,072	4,754
Parent Company | Non-bank Subsidiaries
Condensed Balance Sheet Statements, Captions [Line Items]
Investment in and advances to subsidiaries	$ 104	$ 97