Fair Value Measurements (Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Assets:
Available-for-sale debt securities, fair value	$ 36,028	$ 32,830
Trading debt securities	297	287
Equity securities	564	452
Mortgage Servicing Rights	993	938
Derivative assets	1,673	1,114
Total assets	260	249
Commercial
Assets:
Loans held for sale measured at FV	0	7
Fair value, recurring
Assets:
Available-for-sale debt securities, fair value	35,472	32,278
Trading debt securities	297	287
Equity securities	564	452
Mortgage Servicing Rights	993	938
Derivative assets	1,673	1,114
Total assets	40,446	35,792
Liabilities:
Derivative liabilities	741	874
Short positions	149	138
Total liabilities	890	1,012
Fair value, recurring | Residential Mortgage Loans
Assets:
Loans measured at FV	183
Interest Rate Contract | Fair value, recurring
Assets:
Derivative assets	1,237	655
Liabilities:
Derivative liabilities	157	329
Foreign Exchange Contract | Fair value, recurring
Assets:
Derivative assets	165	152
Liabilities:
Derivative liabilities	151	142
Equity Contract | Fair value, recurring
Liabilities:
Derivative liabilities	163	125
Commodity Contract | Fair value, recurring
Assets:
Derivative assets	271	307
Liabilities:
Derivative liabilities	270	278
Residential mortgage-backed securities | Fair value, recurring
Assets:
Residential mortgage loans held for sale	1,264	537
Loans measured at FV		179
Commercial mortgage-backed securities | Fair value, recurring
Assets:
Loans held for sale measured at FV		7
U.S. Treasury and federal agencies
Assets:
Available-for-sale debt securities, fair value	75	97
U.S. Treasury and federal agencies | Fair value, recurring
Assets:
Available-for-sale debt securities, fair value	75	97
Trading debt securities	2	16
Obligations of states and political subdivisions
Assets:
Available-for-sale debt securities, fair value	18	2
Obligations of states and political subdivisions | Fair value, recurring
Assets:
Available-for-sale debt securities, fair value	18	2
Trading debt securities	9	35
Agency mortgage-backed securities | Fair value, recurring
Assets:
Trading debt securities	55	68
Agency mortgage-backed securities | Fair value, recurring | Commercial
Assets:
Available-for-sale debt securities, fair value	15,693	10,650
Agency mortgage-backed securities | Fair value, recurring | Residential Mortgage Loans
Assets:
Available-for-sale debt securities, fair value	14,115	16,247
Agency mortgage-backed securities | Residential mortgage-backed securities
Assets:
Available-for-sale debt securities, fair value	14,115	16,247
Agency mortgage-backed securities | Commercial mortgage-backed securities
Assets:
Available-for-sale debt securities, fair value	15,693	10,650
Non-agency mortgage-backed securities | Fair value, recurring
Assets:
Available-for-sale debt securities, fair value	3,365	3,267
Non-agency mortgage-backed securities | Commercial mortgage-backed securities
Assets:
Available-for-sale debt securities, fair value	3,365	3,267
Asset-backed securities and other debt securities
Assets:
Available-for-sale debt securities, fair value	2,206	2,015
Asset-backed securities and other debt securities | Fair value, recurring
Assets:
Available-for-sale debt securities, fair value	2,206	2,015
Trading debt securities	231	168
Fair Value, Inputs, Level 1
Assets:
Total assets	0	0
Fair Value, Inputs, Level 1 | Fair value, recurring
Assets:
Available-for-sale debt securities, fair value	75	97
Trading debt securities	2	0
Equity securities	554	452
Mortgage Servicing Rights	0	0
Derivative assets	38	93
Total assets	669	642
Liabilities:
Derivative liabilities	22	27
Short positions	49	110
Total liabilities	71	137
Fair Value, Inputs, Level 1 | Fair value, recurring | Residential Mortgage Loans
Assets:
Loans measured at FV	0
Fair Value, Inputs, Level 1 | Interest Rate Contract | Fair value, recurring
Assets:
Derivative assets	1	0
Liabilities:
Derivative liabilities	5	8
Fair Value, Inputs, Level 1 | Foreign Exchange Contract | Fair value, recurring
Assets:
Derivative assets	0	0
Liabilities:
Derivative liabilities	0	0
Fair Value, Inputs, Level 1 | Equity Contract | Fair value, recurring
Liabilities:
Derivative liabilities	0	0
Fair Value, Inputs, Level 1 | Commodity Contract | Fair value, recurring
Assets:
Derivative assets	37	93
Liabilities:
Derivative liabilities	17	19
Fair Value, Inputs, Level 1 | Residential mortgage-backed securities | Fair value, recurring
Assets:
Residential mortgage loans held for sale	0	0
Loans measured at FV		0
Fair Value, Inputs, Level 1 | Commercial mortgage-backed securities | Fair value, recurring
Assets:
Loans held for sale measured at FV		0
Fair Value, Inputs, Level 1 | U.S. Treasury and federal agencies | Fair value, recurring
Assets:
Available-for-sale debt securities, fair value	75	97
Trading debt securities	2	0
Fair Value, Inputs, Level 1 | Obligations of states and political subdivisions | Fair value, recurring
Assets:
Available-for-sale debt securities, fair value	0	0
Trading debt securities	0	0
Fair Value, Inputs, Level 1 | Agency mortgage-backed securities | Fair value, recurring
Assets:
Trading debt securities	0	0
Fair Value, Inputs, Level 1 | Agency mortgage-backed securities | Fair value, recurring | Commercial
Assets:
Available-for-sale debt securities, fair value	0	0
Fair Value, Inputs, Level 1 | Agency mortgage-backed securities | Fair value, recurring | Residential Mortgage Loans
Assets:
Available-for-sale debt securities, fair value	0	0
Fair Value, Inputs, Level 1 | Non-agency mortgage-backed securities | Fair value, recurring
Assets:
Available-for-sale debt securities, fair value	0	0
Fair Value, Inputs, Level 1 | Asset-backed securities and other debt securities | Fair value, recurring
Assets:
Available-for-sale debt securities, fair value	0	0
Trading debt securities	0	0
Fair Value, Inputs, Level 2
Assets:
Total assets	11	67
Fair Value, Inputs, Level 2 | Fair value, recurring
Assets:
Available-for-sale debt securities, fair value	35,397	32,181
Trading debt securities	295	287
Equity securities	10	0
Mortgage Servicing Rights	0	0
Derivative assets	1,617	1,014
Total assets	38,583	34,026
Liabilities:
Derivative liabilities	548	714
Short positions	100	28
Total liabilities	648	742
Fair Value, Inputs, Level 2 | Fair value, recurring | Residential Mortgage Loans
Assets:
Loans measured at FV	0
Fair Value, Inputs, Level 2 | Interest Rate Contract | Fair value, recurring
Assets:
Derivative assets	1,218	648
Liabilities:
Derivative liabilities	144	313
Fair Value, Inputs, Level 2 | Foreign Exchange Contract | Fair value, recurring
Assets:
Derivative assets	165	152
Liabilities:
Derivative liabilities	151	142
Fair Value, Inputs, Level 2 | Equity Contract | Fair value, recurring
Liabilities:
Derivative liabilities	0	0
Fair Value, Inputs, Level 2 | Commodity Contract | Fair value, recurring
Assets:
Derivative assets	234	214
Liabilities:
Derivative liabilities	253	259
Fair Value, Inputs, Level 2 | Residential mortgage-backed securities | Fair value, recurring
Assets:
Residential mortgage loans held for sale	1,264	537
Fair Value, Inputs, Level 2 | Commercial mortgage-backed securities | Fair value, recurring
Assets:
Loans held for sale measured at FV		7
Fair Value, Inputs, Level 2 | U.S. Treasury and federal agencies | Fair value, recurring
Assets:
Available-for-sale debt securities, fair value	0	0
Trading debt securities	0	16
Fair Value, Inputs, Level 2 | Obligations of states and political subdivisions | Fair value, recurring
Assets:
Available-for-sale debt securities, fair value	18	2
Trading debt securities	9	35
Fair Value, Inputs, Level 2 | Agency mortgage-backed securities | Fair value, recurring
Assets:
Trading debt securities	55	68
Fair Value, Inputs, Level 2 | Agency mortgage-backed securities | Fair value, recurring | Commercial
Assets:
Available-for-sale debt securities, fair value	15,693	10,650
Fair Value, Inputs, Level 2 | Agency mortgage-backed securities | Fair value, recurring | Residential Mortgage Loans
Assets:
Available-for-sale debt securities, fair value	14,115	16,247
Fair Value, Inputs, Level 2 | Non-agency mortgage-backed securities | Fair value, recurring
Assets:
Available-for-sale debt securities, fair value	3,365	3,267
Fair Value, Inputs, Level 2 | Asset-backed securities and other debt securities | Fair value, recurring
Assets:
Available-for-sale debt securities, fair value	2,206	2,015
Trading debt securities	231	168
Fair Value, Inputs, Level 3
Assets:
Total assets	249	182
Fair Value, Inputs, Level 3 | Fair value, recurring
Assets:
Available-for-sale debt securities, fair value	0	0
Trading debt securities	0	0
Equity securities	0	0
Mortgage Servicing Rights	993	938
Derivative assets	18	7
Total assets	1,194	1,124
Liabilities:
Derivative liabilities	171	133
Short positions	0	0
Total liabilities	171	133
Fair Value, Inputs, Level 3 | Fair value, recurring | Residential Mortgage Loans
Assets:
Loans measured at FV	183
Fair Value, Inputs, Level 3 | Interest Rate Contract | Fair value, recurring
Assets:
Derivative assets	18	7
Liabilities:
Derivative liabilities	8	8
Fair Value, Inputs, Level 3 | Foreign Exchange Contract | Fair value, recurring
Assets:
Derivative assets	0	0
Liabilities:
Derivative liabilities	0	0
Fair Value, Inputs, Level 3 | Equity Contract | Fair value, recurring
Liabilities:
Derivative liabilities	163	125
Fair Value, Inputs, Level 3 | Commodity Contract | Fair value, recurring
Assets:
Derivative assets	0	0
Liabilities:
Derivative liabilities	0	0
Fair Value, Inputs, Level 3 | Residential mortgage-backed securities | Fair value, recurring
Assets:
Residential mortgage loans held for sale	0	0
Loans measured at FV		179
Fair Value, Inputs, Level 3 | Commercial mortgage-backed securities | Fair value, recurring
Assets:
Loans held for sale measured at FV		0
Fair Value, Inputs, Level 3 | U.S. Treasury and federal agencies | Fair value, recurring
Assets:
Available-for-sale debt securities, fair value	0	0
Trading debt securities	0	0
Fair Value, Inputs, Level 3 | Obligations of states and political subdivisions | Fair value, recurring
Assets:
Available-for-sale debt securities, fair value	0	0
Trading debt securities	0	0
Fair Value, Inputs, Level 3 | Agency mortgage-backed securities | Fair value, recurring
Assets:
Trading debt securities	0	0
Fair Value, Inputs, Level 3 | Agency mortgage-backed securities | Fair value, recurring | Commercial
Assets:
Available-for-sale debt securities, fair value	0	0
Fair Value, Inputs, Level 3 | Agency mortgage-backed securities | Fair value, recurring | Residential Mortgage Loans
Assets:
Available-for-sale debt securities, fair value	0	0
Fair Value, Inputs, Level 3 | Non-agency mortgage-backed securities | Fair value, recurring
Assets:
Available-for-sale debt securities, fair value	0	0
Fair Value, Inputs, Level 3 | Asset-backed securities and other debt securities | Fair value, recurring
Assets:
Available-for-sale debt securities, fair value	0	0
Trading debt securities	$ 0	$ 0