Pension and Other Postretirement Employee Benefit Plans - Net Periodic Benefit Costs (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Pension plans
Components of net periodic benefit cost
Benefits earned during the period	$ 88	$ 88	$ 266	$ 267
Interest cost on benefit obligations	148	139	447	417
Expected return on plan assets	(227)	(246)	(686)	(741)
Amortization:
Net (gain)/loss	42	26	125	78
Prior service (credit)/cost	0	(7)	2	(19)
Net periodic defined benefit cost	51	0	154	2
Other defined benefit pension plans	7	6	20	21
Total defined benefit plans	58	6	174	23
Total defined contribution plans	255	229	718	661
Total pension and OPEB cost included in noninterest expense	313	235	892	684
OPEB plans
Components of net periodic benefit cost
Benefits earned during the period	0	0	0	0
Interest cost on benefit obligations	6	6	18	18
Expected return on plan assets	(28)	(25)	(84)	(77)
Amortization:
Net (gain)/loss	0	0	0	0
Prior service (credit)/cost	0	0	0	0
Net periodic defined benefit cost	(22)	(19)	(66)	(59)
Total defined benefit plans	(22)	(19)	(66)	(59)
Total pension and OPEB cost included in noninterest expense	$ (22)	$ (19)	$ (66)	$ (59)