Assets and Liabilities Measured at Fair Value on a Recurring Basis (Additional Information) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Other Comprehensive Income (Loss), Unrealized Credit Risk Gain (Loss) on Long-term Debt Arising During Period, Net of Tax	$ (1)	$ (2)
Loans Receivable, Fair Value Disclosure	221		$ 222
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Loans Receivable, Fair Value Disclosure	0		0
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Loans Receivable, Fair Value Disclosure	0		0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Loans Receivable, Fair Value Disclosure	221		222
Total Return Swap [Member] | Fair Value, Inputs, Level 2 [Member]
Loans Receivable, Fair Value Disclosure	2,100		2,100
Equity Funds [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Investments, Fair Value Disclosure	119		102
Investment in Federal Home Loan Bank Stock [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Investments, Fair Value Disclosure	111		132
Federal Reserve Bank Stock [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Investments, Fair Value Disclosure	402		402
Equity Securities [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Investments, Fair Value Disclosure	6		6
Trading Securities [Member] | Commercial and Corporate Leveraged Loans [Member] | Fair Value, Inputs, Level 2 [Member]
Loans Receivable, Fair Value Disclosure	$ 459		$ 356