Benefit Plans - Summary of the Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Net periodic pension cost:
Service cost	$ 238	$ 200	$ 186
Interest cost	201	192	181
Estimated return on plan assets	(448)	(372)	(326)
Amortization and other	81	75	80
Net periodic benefit cost	$ 72	95	121
Income statement location of interest cost	us-gaap:OtherNoninterestExpense
Income statement location of estimated return on plan assets	us-gaap:OtherNoninterestExpense
Income statement location of amortization and other	us-gaap:OtherNoninterestExpense
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income (Loss) [Abstract]
Prior service credit (cost)	$ 0	30	0
Net actuarial loss (gain)	289	137	138
Net amortization	(81)	(75)	(80)
Net amount recognized in OCI	208	92	58
Total net periodic pension costs (income) recognized in total comprehensive income, pre-tax	$ 280	$ 187	$ 179
Weighted average assumptions used to determine net periodic pension cost:
Discount rate	3.79%	4.43%	4.68%
Expected long-term rate of return on plan assets	7.00%	7.00%	7.00%
Assumed long-term rate of annual compensation increases	4.50%	4.50%	4.50%