Pension and Other Postretirement Employee Benefit Plans - Net Periodic Benefit Costs (Details) - USD ($) $ in Millions		12 Months Ended
	Nov. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Health care cost trend rate
Assumed for next year		5.00%	5.00%	5.50%
Ultimate		5.00%	5.00%	5.00%
Year when rate will reach ultimate		2018	2017	2017
U.S.
Weighted-average assumptions used to determine net periodic benefit costs
Rate of compensation increase		2.30%	2.30%	3.50%
Pension plans
Components of net periodic benefit cost
Benefits earned during the year		$ 354	$ 330	$ 332
Interest cost on benefit obligations		556	598	629
Expected return on plan assets		(981)	(968)	(1,030)
Amortization:
Net (gain)/loss		103	250	257
Prior service cost/(credit)		(23)	(36)	(36)
Curtailment (gain)/loss		21	0	0
Settlement (gain)/loss		2	2	4
Net periodic defined benefit cost(a)		32	176	156
Other defined benefit pension plans		20	24	25
Total defined benefit plans		52	200	181
Total defined contribution plans		872	814	789
Total pension and OPEB cost included in noninterest expense		924	1,014	970
Changes in plan assets and benefit obligations recognized in other comprehensive income
Prior service (credit)/cost arising during the year		29	0	0
Net (gain)/loss arising during the year		467	(669)	395
Amortization of net loss		(103)	(250)	(257)
Amortization of prior service (cost)/credit		23	36	36
Curtailment gain/(loss)		(21)	0	0
Settlement gain/(loss)		(2)	(2)	(4)
Foreign exchange impact and other		(30)	54	(77)
Total recognized in other comprehensive income		363	(831)	93
Total recognized in net periodic benefit cost and other comprehensive income		$ 395	$ (655)	$ 249
Pension plans | U.S.
Amortization:
Curtailment (gain)/loss	$ (21)
Pension plans | Minimum
Weighted-average assumptions used to determine net periodic benefit costs
Discount rate		0.60%	0.60%	0.90%
Expected long-term rate of return on plan assets		0.70%	0.70%	0.80%
Rate of compensation increase		2.25%	2.25%	2.25%
Interest crediting rate		1.81%	1.81%	1.56%
Pension plans | Maximum
Weighted-average assumptions used to determine net periodic benefit costs
Discount rate		4.50%	4.30%	4.50%
Expected long-term rate of return on plan assets		5.50%	6.00%	6.50%
Rate of compensation increase		3.00%	3.00%	4.30%
Interest crediting rate		4.90%	4.90%	4.90%
OPEB plans
Components of net periodic benefit cost
Benefits earned during the year		$ 0	$ 0	$ 0
Interest cost on benefit obligations		24	28	31
Expected return on plan assets		(103)	(97)	(105)
Amortization:
Net (gain)/loss		0	0	0
Prior service cost/(credit)		0	0	0
Curtailment (gain)/loss		0	0	0
Settlement (gain)/loss		0	0	0
Net periodic defined benefit cost(a)		(79)	(69)	(74)
Total defined benefit plans		(79)	(69)	(74)
Total pension and OPEB cost included in noninterest expense		(79)	(69)	(74)
Changes in plan assets and benefit obligations recognized in other comprehensive income
Prior service (credit)/cost arising during the year		0	0	0
Net (gain)/loss arising during the year		91	(133)	(29)
Amortization of net loss		0	0	0
Amortization of prior service (cost)/credit		0	0	0
Curtailment gain/(loss)		0	0	0
Settlement gain/(loss)		0	0	0
Foreign exchange impact and other		(4)	0	0
Total recognized in other comprehensive income		87	(133)	(29)
Total recognized in net periodic benefit cost and other comprehensive income		$ 8	$ (202)	$ (103)
Weighted-average assumptions used to determine net periodic benefit costs
Discount rate		3.70%	4.20%	4.40%
Expected long-term rate of return on plan assets		4.00%	5.00%	5.75%