Fair Value Disclosures - Financial Assets and Liabilities Not Recorded at Fair Value (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Financial assets:
HTM securities	$ 20,263	$ 22,837
Loans and leases HFI, net of ALLL	145,152	142,211
Financial liabilities:
Time deposits	12,723	13,170
Long-term debt	23,236	23,648
Carrying Amount
Financial assets:
HTM securities	21,082	23,027
Loans and leases HFI, net of ALLL	145,152	142,211
Financial liabilities:
Time deposits	12,723	13,170
Long-term debt	23,236	23,648
Fair Value | Level 2
Financial assets:
HTM securities	20,263	22,837
Financial liabilities:
Time deposits	12,815	13,266
Long-term debt	23,431	23,885
Fair Value | Level 3
Financial assets:
Loans and leases HFI, net of ALLL	$ 143,151	$ 141,664