Derivative Instruments (Narrative) (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Derivative [Line Items]
Maximum amount of future guarantee payments	$ 637
Cash collateral posted to derivative counterparties	1	$ 50
Securities posted as collateral to derivative counterparties	276	259
Fair value of Credit Support Annex	3	3
Amount of counterparty netting (assets)	0	1
Derivative assets, after counterparty netting	25	19
Other assets and other assets of consolidated VIEs, after counterparty netting and embedded reclass	23	14
Amount of counterparty netting (liabilities)	1	1
Derivative liabilities, after counterparty netting and posting of cash collateral	316	374
Derivative liabilities and derivative liabilities of consolidated VIEs, after counterparty netting and embedded reclass	299	359
Derivative Liabilities [Member]
Derivative [Line Items]
Cash collateral posted to derivative counterparties	0	31
Other Liabilities [Member]
Derivative [Line Items]
Cash collateral posted to derivative counterparties	1	19
Other Assets [Member]
Derivative [Line Items]
Cash collateral posted to derivative counterparties		0
Medium Term Notes And Other Investments [Member] | Embedded [Member]
Derivative [Line Items]
Embedded derivative assets	2	5
Embedded derivative liabilities	$ 17	$ 15