Debt (Principal Payments For Investment Agreements, MTNs and VIE Obligations) (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
2022		$ 265
Thereafter		1,248
Total		1,513
Accrued interest		624	$ 506
Investment Agreement Obligations [Member]
Debt Instrument [Line Items]
2018		17
2019		7
2020		35
2021		3
2022		3
Thereafter		328
Total expected principal payments	[1]	393
Less discount and other adjustments	[2]	56
Total		337
Less unamortized discount		61
Accrued interest		$ 5
Latest maturity year		2037
Medium Term Notes [Member]
Debt Instrument [Line Items]
2018		$ 36
2019		61
2020		0
2021		0
2022		121
Thereafter		847
Total expected principal payments	[3]	1,065
Less discount and other adjustments	[4]	300
Total		765
Less unamortized discount		240
Accrued interest		5
Fair value adjustments		$ 65
Latest maturity year		2036
Variable Interest Entity Debt [Member] | International And Structured Finance Insurance [Member]
Debt Instrument [Line Items]
2018		$ 203
2019		147
2020		485
2021		132
2022		116
Thereafter		1,206
Total expected principal payments	[5]	2,289
Net fair value		$ 1,100
Latest maturity year		2052

[1] Amounts reflect principal due at maturity for investment agreements issued at a discount.

[2] Includes discounts net of carrying amount adjustments of $66 million, net of accrued interest of $5 million.

[3] Amounts reflect principal due at maturity for notes issued at a discount.

[4] Includes discounts net of carrying amount adjustments and embedded derivatives of $279 million, fair value adjustments of $57 million, net of accrued interest of $3 million.

[5] Includes $1.1 billion of VIE notes accounted for at fair value as of December 31, 2016.