Significant Inputs Considered in Determining the Measurement of Credit Losses Recognized in Earnings for Securities (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2016
Investment [Line Items]
Available-for-sale Securities		$ 27,825		$ 30,672
Other than Temporary Impairment Losses, Investments, Available-for-sale Securities, Portion Recognized in Earnings, Net, Qualitative Disclosures, Default Rate	[1]	9.00%	2.00%
Inputs Considered in Determining Measurement of AFS Securities Credit Losses Recognized in Earnings Prepayment Rate	[1]	13.00%	16.00%
Inputs Considered in Determining Measurement of AFS Securities Credit Losses Recognized in Earnings, Loss Severity	[1]	56.00%	46.00%
Mortgage-backed Securities, Issued by Private Enterprises [Member]
Investment [Line Items]
Available-for-sale Securities		$ 94		$ 74
Mortgage-backed Securities, Issued by Private Enterprises [Member] | Other Than Temporarily Impaired Securities [Member]
Investment [Line Items]
Available-for-sale Securities		$ 20	$ 16

[1] For the year ended December 31, 2015, all OTTI credit losses recognized in earnings related to one non-agency MBS with a fair value of approximately $20 million at December 31, 2015. For the year ended December 31, 2014, all OTTI credit losses recognized in earnings related to one non-agency MBS with a fair value of $16 million at December 31, 2014.