Pension and Other Postretirement Employee Benefit Plans - Net Periodic Benefit Costs (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Pension plans
Components of net periodic benefit cost
Benefits earned during the period	$ 89	$ 89	$ 178	$ 179
Interest cost on benefit obligations	149	139	299	278
Expected return on plan assets	(229)	(247)	(459)	(495)
Amortization:
Net (gain)/loss	41	26	83	52
Prior service (credit)/cost	1	(6)	2	(12)
Net periodic defined benefit cost	51	1	103	2
Other defined benefit pension plans	7	9	13	15
Total defined benefit plans	58	10	116	17
Total defined contribution plans	243	222	463	432
Total pension and OPEB cost included in noninterest expense	301	232	579	449
OPEB plans
Components of net periodic benefit cost
Benefits earned during the period	0	0	0	0
Interest cost on benefit obligations	6	6	12	12
Expected return on plan assets	(28)	(26)	(56)	(52)
Amortization:
Net (gain)/loss	0	0	0	0
Prior service (credit)/cost	0	0	0	0
Net periodic defined benefit cost	(22)	(20)	(44)	(40)
Total defined benefit plans	(22)	(20)	(44)	(40)
Total pension and OPEB cost included in noninterest expense	$ (22)	$ (20)	$ (44)	$ (40)