Pension and Other Postretirement Employee Benefit Plans - Net Periodic Benefit Costs (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Defined benefit pension plans
Components of net periodic benefit cost
Benefits earned during the period	$ 88	$ 83	$ 267	$ 247
Interest cost on benefit obligations	139	148	417	447
Expected return on plan assets	(246)	(242)	(741)	(725)
Amortization:
Net (gain)/loss	26	63	78	187
Prior service cost/(credit)	(7)	(9)	(19)	(27)
Settlement	0	0	0	(3)
Net periodic defined benefit cost	0	43	2	126
Other defined benefit pension plans	6	6	21	16
Total defined benefit plans	6	49	23	142
Total defined contribution plans	229	221	661	617
Total pension and OPEB cost included in noninterest expense	235	270	684	759
OPEB plans
Components of net periodic benefit cost
Benefits earned during the period	0	0	0	0
Interest cost on benefit obligations	6	7	18	21
Expected return on plan assets	(25)	(24)	(77)	(72)
Amortization:
Net (gain)/loss	0	0	0	0
Prior service cost/(credit)	0	0	0	0
Settlement	0	0	0	0
Net periodic defined benefit cost	(19)	(17)	(59)	(51)
Total defined benefit plans	(19)	(17)	(59)	(51)
Total pension and OPEB cost included in noninterest expense	$ (19)	$ (17)	$ (59)	$ (51)