Fair Value Disclosures - Financial Assets and Liabilities Not Recorded at Fair Value (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Financial assets:
HTM securities	$ 22,390	$ 23,027
Loans and leases HFI, net of ALLL	141,519	142,211
Financial liabilities:
Time deposits	13,725	13,170
Long-term debt	23,410	23,648
Carrying Amount
Financial assets:
HTM securities	22,390	23,027
Loans and leases HFI, net of ALLL	141,519	142,211
Financial liabilities:
Time deposits	13,725	13,170
Long-term debt	23,410	23,648
Fair Value | Level 2
Financial assets:
HTM securities	21,829	22,837
Financial liabilities:
Time deposits	13,775	13,266
Long-term debt	23,495	23,885
Fair Value | Level 3
Financial assets:
Loans and leases HFI, net of ALLL	$ 140,461	$ 141,664