Carrying Amounts and Fair Values of the Company's Financial Instruments (Detail) - USD ($)		Sep. 30, 2018		Dec. 31, 2017
Financial assets
Debt Securities, Trading, and Equity Securities, FV-NI	[1]	$ 5,676,000,000		$ 5,093,000,000
Available-for-sale Securities	[2],[3]	30,984,000,000		30,947,000,000	[4]
Debt Securities, Held-to-maturity, Fair Value		0		0
Loans Receivable Held-for-sale, Net, Not Part of Disposal Group	[5]	1,961,000,000		2,290,000,000
Loans Held-for-sale, Fair Value Disclosure		1,822,000,000		1,577,000,000
Loans and Leases Receivable, Excluding Fair Value Loans		147,047,000,000		142,985,000,000
Loans Receivable, Fair Value Disclosure		168,000,000		196,000,000
Other Assets	[2]	9,432,000,000		9,418,000,000
Other Assets, Fair Value Disclosure				56,000,000
Financial liabilities
Deposits		160,378,000,000		160,780,000,000
Long-term Debt	[6]	14,289,000,000		9,785,000,000
Fair Value, Inputs, Level 1 [Member]
Financial assets
Cash and Cash Equivalents, Fair Value Disclosure		7,605,000,000		6,912,000,000
Debt Securities, Trading, and Equity Securities, FV-NI		638,000,000		608,000,000
Available-for-sale Securities		4,133,000,000		4,331,000,000
Loans Receivable Held-for-sale, Net, Not Part of Disposal Group		0		0
Loans Held-for-sale, Fair Value Disclosure		0		0
Loans and Leases Receivable, Excluding Fair Value Loans		0		0
Loans Receivable, Fair Value Disclosure		0		0
Other Assets		0		0
Other Assets, Fair Value Disclosure		92,000,000		56,000,000
Financial liabilities
Time Deposits		0		0
Short-term Debt, Fair Value		0		0
Long-term Debt		0		0
Long-term Debt, Fair Value		0		0
Trading liabilities		886,000,000		769,000,000
Fair Value, Inputs, Level 2 [Member]
Financial assets
Cash and Cash Equivalents, Fair Value Disclosure		0		0
Debt Securities, Trading, and Equity Securities, FV-NI		5,026,000,000		4,469,000,000
Available-for-sale Securities		26,851,000,000		26,544,000,000
Loans Receivable Held-for-sale, Net, Not Part of Disposal Group		110,000,000		662,000,000
Loans Held-for-sale, Fair Value Disclosure		1,822,000,000		1,577,000,000
Loans and Leases Receivable, Excluding Fair Value Loans		0		0
Loans Receivable, Fair Value Disclosure		0		0
Other Assets		0		0
Other Assets, Fair Value Disclosure		0		0
Financial liabilities
Time Deposits		14,889,000,000		11,906,000,000
Short-term Debt, Fair Value		7,940,000,000		4,781,000,000
Long-term Debt		12,396,000,000		8,304,000,000
Long-term Debt, Fair Value		235,000,000		530,000,000
Trading liabilities		968,000,000		498,000,000
Fair Value, Inputs, Level 3 [Member]
Financial assets
Cash and Cash Equivalents, Fair Value Disclosure		0		0
Debt Securities, Trading, and Equity Securities, FV-NI		12,000,000		16,000,000
Available-for-sale Securities		0		72,000,000
Loans Receivable Held-for-sale, Net, Not Part of Disposal Group		32,000,000		54,000,000
Loans Held-for-sale, Fair Value Disclosure		0		0
Loans and Leases Receivable, Excluding Fair Value Loans		144,480,000,000		141,379,000,000
Loans Receivable, Fair Value Disclosure		168,000,000		196,000,000
Other Assets		545,000,000		418,000,000
Other Assets, Fair Value Disclosure		0		0
Financial liabilities
Time Deposits		0		0
Short-term Debt, Fair Value		0		0
Long-term Debt		1,729,000,000		1,058,000,000
Long-term Debt, Fair Value		0		0
Trading liabilities		9,000,000		16,000,000
Reported Value Measurement [Member]
Financial assets
Cash and Cash Equivalents, Fair Value Disclosure		7,605,000,000		6,912,000,000
Debt Securities, Trading, and Equity Securities, FV-NI		5,676,000,000		5,093,000,000
Available-for-sale Securities		30,984,000,000		30,947,000,000
Loans Receivable Held-for-sale, Net, Not Part of Disposal Group		139,000,000		713,000,000
Loans Held-for-sale, Fair Value Disclosure		1,822,000,000		1,577,000,000
Loans and Leases Receivable, Excluding Fair Value Loans		145,424,000,000		141,250,000,000
Loans Receivable, Fair Value Disclosure		168,000,000		196,000,000
Other Assets		545,000,000	[7]	418,000,000	[8]
Other Assets, Fair Value Disclosure		92,000,000	[7]	56,000,000	[8]
Financial liabilities
Time Deposits		15,166,000,000		12,076,000,000
Short-term Debt, Fair Value		7,940,000,000		4,781,000,000
Long-term Debt		14,054,000,000		9,255,000,000
Long-term Debt, Fair Value		235,000,000		530,000,000
Trading liabilities		1,863,000,000		1,283,000,000
Estimate of Fair Value, Fair Value Disclosure [Member]
Financial assets
Cash and Cash Equivalents, Fair Value Disclosure		7,605,000,000		6,912,000,000
Debt Securities, Trading, and Equity Securities, FV-NI		5,676,000,000		5,093,000,000
Available-for-sale Securities		30,984,000,000		30,947,000,000
Loans Receivable Held-for-sale, Net, Not Part of Disposal Group		142,000,000		716,000,000
Loans Held-for-sale, Fair Value Disclosure		1,822,000,000		1,577,000,000
Loans and Leases Receivable, Excluding Fair Value Loans		144,480,000,000		141,379,000,000
Loans Receivable, Fair Value Disclosure		168,000,000		196,000,000
Other Assets		545,000,000	[7]	418,000,000	[8]
Other Assets, Fair Value Disclosure		92,000,000	[7]	56,000,000	[8]
Financial liabilities
Time Deposits		14,889,000,000		11,906,000,000
Short-term Debt, Fair Value		7,940,000,000		4,781,000,000
Long-term Debt		14,125,000,000		9,362,000,000
Long-term Debt, Fair Value		235,000,000		530,000,000
Trading liabilities		1,863,000,000		1,283,000,000
Brokered Time Deposits [Member] | Fair Value, Inputs, Level 1 [Member]
Financial liabilities
Deposits		0		0
Deposits, Fair Value Disclosure		0		0
Brokered Time Deposits [Member] | Fair Value, Inputs, Level 2 [Member]
Financial liabilities
Deposits		738,000,000		725,000,000
Deposits, Fair Value Disclosure		384,000,000		236,000,000
Brokered Time Deposits [Member] | Fair Value, Inputs, Level 3 [Member]
Financial liabilities
Deposits		0		0
Deposits, Fair Value Disclosure		0		0
Brokered Time Deposits [Member] | Reported Value Measurement [Member]
Financial liabilities
Deposits		662,000,000		749,000,000
Deposits, Fair Value Disclosure		384,000,000		236,000,000
Brokered Time Deposits [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Financial liabilities
Deposits		738,000,000		725,000,000
Deposits, Fair Value Disclosure		$ 384,000,000		$ 236,000,000

[1] Includes trading securities pledged as collateral where counterparties have the right to sell or repledge the collateral of $1,362 million and $1,086 million at September 30, 2018 and December 31, 2017, respectively.

[2] 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.

[3] Includes securities AFS pledged as collateral where counterparties have the right to sell or repledge the collateral of $164 million and $223 million at September 30, 2018 and December 31, 2017, respectively.

[4] Beginning January 1, 2018, the Company reclassified equity securities previously presented in Securities available for sale to Other assets on the Consolidated Balance Sheets. Reclassifications have been made to previously reported amounts for comparability. See Note 9, "Other Assets," for additional information.

[5] Includes $1.8 billion and $1.6 billion of LHFS measured at fair value at September 30, 2018 and December 31, 2017, respectively.

[6] Includes debt of consolidated VIEs of $168 million and $189 million at September 30, 2018 and December 31, 2017, respectively.

[7] Other financial assets recorded at amortized cost consist of FHLB of Atlanta stock and Federal Reserve Bank of Atlanta stock. Other financial assets recorded at fair value consist of mutual fund investments and other equity securities with readily determinable fair values.

[8] Other financial assets recorded at amortized cost consist of FHLB of Atlanta stock and Federal Reserve Bank of Atlanta stock. Other financial assets recorded at fair value consist of mutual fund investments and other equity securities with readily determinable fair values.