Derivative Instruments (Narrative) (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Derivative [Line Items]
Maximum amount of future guarantee payments	$ 3,400
Cash collateral posted to derivative counterparties	50	$ 12
Securities posted as collateral to derivative counterparties	$ 259	$ 198
Number of credit support annexes	1	1
Fair value of Credit Support Annex	$ 3	$ 2
Amount of counterparty netting	1	81
Derivative assets, after counterparty netting	19	10
Other assets and other assets of consolidated VIEs, after counterparty netting and embedded reclass	14	2
Counterparty netting	1	81
Derivative liabilities, after counterparty netting and posting of cash collateral	374	456
Derivative liabilities and derivative liabilities of consolidated VIEs, after counterparty netting and embedded reclass	359	437
Derivative Liabilities [Member]
Derivative [Line Items]
Cash collateral posted to derivative counterparties	31	0
Other Liabilities [Member]
Derivative [Line Items]
Cash collateral posted to derivative counterparties	19	12
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	5	8
Total derivative liabilities	$ 15	$ 19