Securities (Tables)

12 Months Ended

Dec. 31, 2017

Investments, Debt and Equity Securities [Abstract]

Summary of Amortized Cost, Gross Unrealized Gains and Approximate Fair Values of AFS Securities

The amortized cost and fair value of the securities portfolio are presented in the following tables:

December 31, 2017	Amortized Cost		Gross Unrealized				Fair Value
(Dollars in millions)			Gains		Losses
AFS securities:
U.S. Treasury	$	2,368	$	—	$	77	$	2,291
GSE	187		—		8		179
Agency MBS	20,683		8		590		20,101
States and political subdivisions	1,379		37		24		1,392
Non-agency MBS	384		192		—		576
Other	8		—		—		8
Total AFS securities	$	25,009	$	237	$	699	$	24,547
HTM securities:
U.S. Treasury	$	1,098	$	8	$	—	$	1,106
GSE	2,198		11		22		2,187
Agency MBS	19,660		33		222		19,471
States and political subdivisions	28		—		—		28
Other	43		2		—		45
Total HTM securities	$	23,027	$	54	$	244	$	22,837

December 31, 2016	Amortized Cost		Gross Unrealized				Fair Value
(Dollars in millions)			Gains		Losses
AFS securities:
U.S. Treasury	$	2,669	$	2	$	84	$	2,587
GSE	190		—		10		180
Agency MBS	21,819		13		568		21,264
States and political subdivisions	2,198		56		49		2,205
Non-agency MBS	446		233		—		679
Other	11		—		—		11
Total AFS securities	$	27,333	$	304	$	711	$	26,926
HTM securities:
U.S. Treasury	$	1,098	$	20	$	—	$	1,118
GSE	2,197		14		30		2,181
Agency MBS	13,225		40		180		13,085
States and political subdivisions	110		—		—		110
Other	50		2		—		52
Total HTM securities	$	16,680	$	76	$	210	$	16,546

Summary of Summary of Amortized Cost, Gross Unrealized Gains and Approximate Fair Values of HTM Securities

The amortized cost and fair value of the securities portfolio are presented in the following tables:

December 31, 2017	Amortized Cost		Gross Unrealized				Fair Value
(Dollars in millions)			Gains		Losses
AFS securities:
U.S. Treasury	$	2,368	$	—	$	77	$	2,291
GSE	187		—		8		179
Agency MBS	20,683		8		590		20,101
States and political subdivisions	1,379		37		24		1,392
Non-agency MBS	384		192		—		576
Other	8		—		—		8
Total AFS securities	$	25,009	$	237	$	699	$	24,547
HTM securities:
U.S. Treasury	$	1,098	$	8	$	—	$	1,106
GSE	2,198		11		22		2,187
Agency MBS	19,660		33		222		19,471
States and political subdivisions	28		—		—		28
Other	43		2		—		45
Total HTM securities	$	23,027	$	54	$	244	$	22,837

December 31, 2016	Amortized Cost		Gross Unrealized				Fair Value
(Dollars in millions)			Gains		Losses
AFS securities:
U.S. Treasury	$	2,669	$	2	$	84	$	2,587
GSE	190		—		10		180
Agency MBS	21,819		13		568		21,264
States and political subdivisions	2,198		56		49		2,205
Non-agency MBS	446		233		—		679
Other	11		—		—		11
Total AFS securities	$	27,333	$	304	$	711	$	26,926
HTM securities:
U.S. Treasury	$	1,098	$	20	$	—	$	1,118
GSE	2,197		14		30		2,181
Agency MBS	13,225		40		180		13,085
States and political subdivisions	110		—		—		110
Other	50		2		—		52
Total HTM securities	$	16,680	$	76	$	210	$	16,546

Schedule of Amortized Cost and Estimated Fair Value by Contractual Maturity

The amortized cost and estimated fair value of the securities portfolio by contractual maturity are shown in the following table. The expected life of MBS may differ from contractual maturities because borrowers have the right to prepay the underlying mortgage loans with or without prepayment penalties.

	AFS				HTM
December 31, 2017	Amortized Cost		Fair Value		Amortized Cost		Fair Value
(Dollars in millions)
Due in one year or less	$	336	$	335	$	—	$	—
Due after one year through five years	498		496		2,237		2,242
Due after five years through ten years	2,419		2,341		1,111		1,103
Due after ten years	21,756		21,375		19,679		19,492
Total debt securities	$	25,009	$	24,547	$	23,027	$	22,837

Schedule of Fair Values and Gross Unrealized Losses of Investments by Investment Category and Length of Time

The following tables present the fair values and gross unrealized losses of investments based on the length of time that individual securities have been in a continuous unrealized loss position:

	Less than 12 months				12 months or more				Total
December 31, 2017	Fair Value		Unrealized Losses		Fair Value		Unrealized Losses		Fair Value		Unrealized Losses
(Dollars in millions)
AFS securities:
U.S. Treasury	$	634	$	4	$	1,655	$	73	$	2,289	$	77
GSE	9		—		170		8		179		8
Agency MBS	5,077		64		13,920		526		18,997		590
States and political subdivisions	201		1		355		23		556		24
Total	$	5,921	$	69	$	16,100	$	630	$	22,021	$	699
HTM securities:
GSE	$	1,470	$	12	$	290	$	10	$	1,760	$	22
Agency MBS	10,880		77		4,631		145		15,511		222
Total	$	12,350	$	89	$	4,921	$	155	$	17,271	$	244

	Less than 12 months				12 months or more				Total
December 31, 2016	Fair Value		Unrealized Losses		Fair Value		Unrealized Losses		Fair Value		Unrealized Losses
(Dollars in millions)
AFS securities:
U.S. Treasury	$	2,014	$	84	$	—	$	—	$	2,014	$	84
GSE	180		10		—		—		180		10
Agency MBS	14,842		342		5,138		226		19,980		568
States and political subdivisions	365		7		314		42		679		49
Total	$	17,401	$	443	$	5,452	$	268	$	22,853	$	711
HTM securities:
GSE	$	1,762	$	30	$	—	$	—	$	1,762	$	30
Agency MBS	7,717		178		305		2		8,022		180
Total	$	9,479	$	208	$	305	$	2	$	9,784	$	210