Parent Company Financial Statements (Condensed Balance Sheet - Parent Company Only) (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Assets
Equity securities	$ 564	$ 452
Investments in subsidiaries:
Goodwill	4,252	2,478	$ 2,445
Other Assets	9,190	7,372
Total Assets	169,369	146,069
Liabilities
Other short-term borrowings	1,011	573
Accrued expenses and other liabilities	2,422	2,498
Long-term debt (external)	14,970	14,426
Total liabilities	148,166	129,819
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest [Abstract]
Common stock	2,051	2,051
Preferred stock	1,770	1,331
Capital surplus	3,599	2,873
Retained earnings	18,315	16,578
Accumulated other comprehensive income (loss)	1,192	(112)	73
Treasury stock	(5,724)	(6,471)
Noncontrolling interests	0	0
Total Equity	21,203	16,250	$ 16,220	$ 16,081
Total Liabilities and Equity	169,369	146,069
Parent Company Only
Assets
Cash	118	120
Short-term Investments	4,723	3,642
Equity securities	49	0
Loans to subsidiaries:
Nonbank subsidiaries	444	571
Total loans to subsidiaries	444	571
Investments in subsidiaries:
Nonbank subsidiaries	23,779	17,921
Total investment in subsidiaries	23,779	17,921
Goodwill	80	80
Other Assets	379	268
Total Assets	29,572	22,602
Liabilities
Other short-term borrowings	359	253
Accrued expenses and other liabilities	497	424
Long-term debt (external)	7,513	5,675
Total liabilities	8,369	6,352
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest [Abstract]
Common stock	2,051	2,051
Preferred stock	1,770	1,331
Capital surplus	3,599	2,873
Retained earnings	18,315	16,578
Accumulated other comprehensive income (loss)	1,192	(112)
Treasury stock	(5,724)	(6,471)
Noncontrolling interests	0	0
Total Equity	21,203	16,250
Total Liabilities and Equity	$ 29,572	$ 22,602