Fair Value Disclosures - Financial Assets and Liabilities Not Recorded at Fair Value (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Financial assets:
HTM securities	$ 21,080	$ 22,837
Loans and leases HFI, net of ALLL	144,653	142,211
Financial liabilities:
Time deposits	14,781	13,170
Long-term debt	24,081	23,648
Carrying Amount
Financial assets:
HTM securities	21,749	23,027
Loans and leases HFI, net of ALLL	144,653	142,211
Financial liabilities:
Time deposits	14,781	13,170
Long-term debt	24,081	23,648
Fair Value | Level 2
Financial assets:
HTM securities	21,080	22,837
Financial liabilities:
Time deposits	14,817	13,266
Long-term debt	24,155	23,885
Fair Value | Level 3
Financial assets:
Loans and leases HFI, net of ALLL	$ 143,345	$ 141,664