Securities with Unrealized Losses (Detail) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2017		Dec. 31, 2016
Investments, Unrealized Loss Position [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 19,130	[1]	$ 19,459	[2]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	362	[3]	383	[4]
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	529	[1]	464	[2]
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	8	[3]	9	[4]
Total, Fair Value	19,659	[1]	19,923	[2]
Total, Unrealized Losses	370	[3]	392	[4]
Temporarily Impaired Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	19,130		19,443
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	362	[3]	383	[4]
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	512		463
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	8	[3]	9	[4]
Total, Fair Value	19,642		19,906
Total, Unrealized Losses	370	[3]	392	[4]
Temporarily Impaired Securities [Member] | US Treasury Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	4,108		4,380
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	71	[3]	86	[4]
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0		0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	0	[3]	0	[4]
Total, Fair Value	4,108		4,380
Total, Unrealized Losses	71	[3]	86	[4]
Temporarily Impaired Securities [Member] | US Government Agencies Debt Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	94		96
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	1	[3]	2	[4]
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	3		3
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	0	[3]	0	[4]
Total, Fair Value	97		99
Total, Unrealized Losses	1	[3]	2	[4]
Temporarily Impaired Securities [Member] | US States and Political Subdivisions Debt Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	147		149
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	4	[3]	5	[4]
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0		0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	0	[3]	0	[4]
Total, Fair Value	147		149
Total, Unrealized Losses	4	[3]	5	[4]
Temporarily Impaired Securities [Member] | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Investments, Unrealized Loss Position [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	14,445		14,622
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	280	[3]	285	[4]
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	500		451
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	7	[3]	8	[4]
Total, Fair Value	14,945		15,073
Total, Unrealized Losses	287	[3]	293	[4]
Temporarily Impaired Securities [Member] | Commercial Mortgage Backed Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	325		184
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	6	[3]	5	[4]
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0		0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	0	[3]	0	[4]
Total, Fair Value	325		184
Total, Unrealized Losses	6	[3]	5	[4]
Temporarily Impaired Securities [Member] | Asset-backed Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	0		0
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	0	[3]	0	[4]
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	5		5
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	0	[3]	0	[4]
Total, Fair Value	5		5
Total, Unrealized Losses	0	[3]	0	[4]
Temporarily Impaired Securities [Member] | Other Debt Obligations [Member]
Investments, Unrealized Loss Position [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	11		12
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	0	[3]	0	[4]
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0		0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	0	[3]	0	[4]
Total, Fair Value	11		12
Total, Unrealized Losses	0	[3]	0	[4]
Temporarily Impaired Securities [Member] | Equity Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	0		0
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	0	[3]	0	[4]
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	4		4
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	1	[3]	1	[4]
Total, Fair Value	4		4
Total, Unrealized Losses	1	[3]	1	[4]
Other Than Temporarily Impaired Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	0	[1]	16	[2]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	0	[3]	0	[4]
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	17	[1]	1	[2]
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	0	[3]	0	[4]
Total, Fair Value	17	[1]	17	[2]
Total, Unrealized Losses	0	[3]	0	[4]
Other Than Temporarily Impaired Securities [Member] | Asset-backed Securities [Member]
Investments, Unrealized Loss Position [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	0	[1]	0	[2]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	0	[3]	0	[4]
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	1	[1]	1	[2]
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	0	[3]	0	[4]
Total, Fair Value	1	[1]	1	[2]
Total, Unrealized Losses	0	[3]	0	[4]
Other Than Temporarily Impaired Securities [Member] | Mortgage-backed Securities, Issued by Private Enterprises [Member]
Investments, Unrealized Loss Position [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	0	[1]	16	[2]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Aggregate Loss	0	[3]	0	[4]
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	16	[1]	0	[2]
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	0	[3]	0	[4]
Total, Fair Value	16	[1]	16	[2]
Total, Unrealized Losses	$ 0	[3]	$ 0	[4]

[1] OTTI securities AFS are impaired securities for which OTTI credit losses have been previously recognized in earnings.

[2] OTTI securities AFS are impaired securities for which OTTI credit losses have been previously recognized in earnings.

[3] Unrealized losses less than $0.5 million are presented as zero within the table.

[4] Unrealized losses less than $0.5 million are presented as zero within the table.