Accumulated Other Comprehensive Income - Reclassifications Out of AOCI (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Realized gains	$ 0	$ 1	$ 0
Realized losses	0	0	0
Interest income — Loans	4,023	3,677	2,773
Interest expense — Long-term debt	(420)	(319)	(218)
Investment banking and debt placement fees	650	603	482
Personnel expense	(2,309)	(2,278)	(2,048)
Income (loss) before income taxes and equity in net income (loss) less dividends from subsidiaries	2,234	1,981	1,002
Income taxes	344	637	179
Income (loss) from continuing operations	1,859	1,291	$ 789
Reclassification out of Accumulated Other Comprehensive Income [Member] | Unrealized Gains (Losses) on Securities Available for Sale [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income (loss) before income taxes and equity in net income (loss) less dividends from subsidiaries	0	1
Income taxes	0	0
Income (loss) from continuing operations	0	1
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income (loss) before income taxes and equity in net income (loss) less dividends from subsidiaries	(37)	15
Income taxes	(8)	5
Income (loss) from continuing operations	(29)	10
Reclassification out of Accumulated Other Comprehensive Income [Member] | Foreign Currency Translation Adjustment [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Personnel expense	0	(1)
Income (loss) before income taxes and equity in net income (loss) less dividends from subsidiaries	0	(1)
Income taxes	0	0
Income (loss) from continuing operations	0	(1)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Net Pension and Postretirement Benefit Costs [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income (loss) before income taxes and equity in net income (loss) less dividends from subsidiaries	(33)	(14)
Income taxes	(8)	(5)
Income (loss) from continuing operations	(25)	(9)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Net Pension and Postretirement Benefit Costs [Member] | Amortization of Losses [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Personnel expense	(17)	(15)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Net Pension and Postretirement Benefit Costs [Member] | Settlement Loss [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Personnel expense	17	0
Reclassification out of Accumulated Other Comprehensive Income [Member] | Net Pension and Postretirement Benefit Costs [Member] | Amortization Of Prior Service Credit [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Personnel expense	1	1
Other Income [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Unrealized Gains (Losses) on Securities Available for Sale [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Realized gains	0	1
Realized losses	0	0
Other Income [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent [Member] | Foreign Exchange Contract [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Unrealized gain (loss) on derivatives	31	0
Interest Income [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent [Member] | Interest Rate [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest income — Loans	(68)	19
Interest Expense [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent [Member] | Interest Rate [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest expense — Long-term debt	2	4
Investment Banking And Debt Placement [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent [Member] | Interest Rate [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Investment banking and debt placement fees	$ 2	$ 0