Defined Benefit Plan, Change in Obligations and Fair Value (Additional Information) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017
Other Assets	[1],[2]	$ 8,991	$ 9,099
Other Liabilities		3,226	4,179
Pension Plan [Member]
Liability, Defined Benefit Plan, Current		68	78
Defined Benefit Plan, Plan Assets, Contributions by Employer	[3]	8	9
Common Stock Held in Pension Plan		0
Other Assets		485	456
Other Liabilities		68	78
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan, Plan Assets, Contributions by Employer	[4]	0	0
Other Assets		$ 104	$ 106

[1] Beginning January 1, 2018, the Company reclassified equity securities previously presented in Securities available for sale to Other assets. Reclassifications have been made to previously reported amounts for comparability.

[2] Beginning October 1, 2018, the Company reclassified software and related accumulated amortization previously presented in Other assets to Premises, property, and equipment, net. Reclassifications have been made to previously reported amounts for comparability.

[3] Employer contributions represent the benefits that were paid to nonqualified plan participants. Unfunded nonqualified supplemental pension plans are not funded through plan assets.

[4] The Company contributed less than $1 million to the other postretirement benefits plans during both 2018 and 2017.