Parent Company Financial Statements - Parent Company Condensed Income and Comprehensive Income Statements (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income:
Interest and other income from subsidiaries	$ 52	$ 52	$ 39
Other income	467	362	326
Expenses:
Interest expense	839	745	735
Other expenses	7,444	6,721	6,266
Income tax benefit	(911)	(1,058)	(794)
Net income	2,415	2,442	2,123
Total OCI	(88)	(104)	(277)
Total comprehensive income	2,327	2,338	1,846
Parent Company
Income:
Dividends from subsidiaries	1,990	1,356	2,011
Interest and other income from subsidiaries	112	73	64
Other income	2	3	3
Total income	2,104	1,432	2,078
Expenses:
Interest expense	227	160	165
Other expenses	83	56	103
Total expenses	310	216	268
Income before income taxes and equity in undistributed earnings of subsidiaries	1,794	1,216	1,810
Income tax benefit	63	38	40
Income before equity in undistributed earnings of subsidiaries	1,857	1,254	1,850
Equity in undistributed earnings of subsidiaries in excess of dividends from subsidiaries	558	1,188	273
Net income	2,415	2,442	2,123
Total OCI	(88)	(104)	(277)
Total comprehensive income	2,327	2,338	1,846
Parent Company | Banking
Income:
Dividends from subsidiaries	1,950	1,350	1,600
Parent Company | Nonbank
Income:
Dividends from subsidiaries	$ 40	$ 6	$ 411