Pension and Other Postretirement Employee Benefit Plans - Net Periodic Benefit Costs (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Pension plans
Components of net periodic benefit cost
Benefits earned during the period	$ 89	$ 90
Interest cost on benefit obligations	150	139
Expected return on plan assets	(230)	(248)
Amortization:
Net (gain)/loss	42	26
Prior service (credit)/cost	1	(6)
Net periodic defined benefit cost	52	1
Other defined benefit pension plans	6	6
Total defined benefit plans	58	7
Total defined contribution plans	220	210
Total pension and OPEB cost included in noninterest expense	278	217
OPEB plans
Components of net periodic benefit cost
Benefits earned during the period	0	0
Interest cost on benefit obligations	6	6
Expected return on plan assets	(28)	(26)
Amortization:
Net (gain)/loss	0	0
Prior service (credit)/cost	0	0
Net periodic defined benefit cost	(22)	(20)
Total defined benefit plans	(22)	(20)
Total pension and OPEB cost included in noninterest expense	$ (22)	$ (20)