Derivative Instruments (Narrative) (Detail) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Derivative [Line Items]
Maximum amount of future guarantee payments	$ 1,300
Cash collateral posted to derivative counterparties	71	$ 50
Securities posted as collateral to derivative counterparties	311	259
Fair value of Credit Support Annex	3	3
Amount of counterparty netting (assets)	0	1
Derivative assets, after counterparty netting	16	19
Other assets and other assets of consolidated VIEs, after counterparty netting and embedded reclass	12	14
Amount of counterparty netting (liabilities)		1
Derivative liabilities, after counterparty netting and posting of cash collateral	398	374
Derivative liabilities and derivative liabilities of consolidated VIEs, after counterparty netting and embedded reclass	378	359
Derivative Liabilities [Member]
Derivative [Line Items]
Cash collateral posted to derivative counterparties	53	31
Other Liabilities [Member]
Derivative [Line Items]
Cash collateral posted to derivative counterparties	18	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	4	5
Embedded derivative liabilities	$ 20	$ 15