Stockholders' Equity - Change in AOCI Gain (Loss) by Component (Net of Tax) (Detail) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
AOCI beginning balance	$ (1,263)	$ (926)
Cumulatrive effects from adoption of new accounting standards	(11)	0
Other comprehensive income (loss) before reclassifications	450	(498)
Net realized (gains) losses reclassified from AOCI into earnings	153	(56)
Other comprehensive income (loss), net of tax	603	(472)
AOCI ending balance	(660)	(1,599)
One time transfer of held to maturity securities	36,503		$ 36,771
Accumulated Net Unrealized Investment Gain (Loss) \| Available-for-sale securities
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
AOCI beginning balance	(439)	17
Cumulatrive effects from adoption of new accounting standards		3
Other comprehensive income (loss) before reclassifications	310	(254)
Net realized (gains) losses reclassified from AOCI into earnings	(18)	(6)
Other comprehensive income (loss), net of tax	292	(585)
AOCI ending balance	(147)	(565)
Accumulated Net Unrealized Investment Gain (Loss) \| Securities Held to Maturity
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
AOCI beginning balance	(190)	(524)
Cumulatrive effects from adoption of new accounting standards		(113)
Other comprehensive income (loss) before reclassifications	0	0
Net realized (gains) losses reclassified from AOCI into earnings	6	18
Other comprehensive income (loss), net of tax	6	425
AOCI ending balance	(184)	(212)
Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
AOCI beginning balance	(418)	(281)
Cumulatrive effects from adoption of new accounting standards		(63)
Other comprehensive income (loss), transfers from held-to-maturity to available-for-sale securities, before tax		0
Other comprehensive income (loss) before reclassifications	111	(251)
Net realized (gains) losses reclassified from AOCI into earnings	166	(67)
Other comprehensive income (loss), net of tax	277	(318)
AOCI ending balance	(141)	(662)
Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
AOCI beginning balance	(177)	(138)
Cumulatrive effects from adoption of new accounting standards		0
Other comprehensive income (loss), transfers from held-to-maturity to available-for-sale securities, before tax		0
Other comprehensive income (loss) before reclassifications	30	7
Net realized (gains) losses reclassified from AOCI into earnings	0	0
Other comprehensive income (loss), net of tax	30	7
AOCI ending balance	(147)	(131)
Other
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
AOCI beginning balance	(39)	0
Cumulatrive effects from adoption of new accounting standards		(28)
Other comprehensive income (loss), transfers from held-to-maturity to available-for-sale securities, before tax		0
Other comprehensive income (loss) before reclassifications	(1)	0
Net realized (gains) losses reclassified from AOCI into earnings	(1)	(1)
Other comprehensive income (loss), net of tax	(2)	(1)
AOCI ending balance	(41)	(29)
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Cumulatrive effects from adoption of new accounting standards		(201)
ASU 2017-12
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
One time transfer of held to maturity securities		9,000
ASU 2017-12 \| Accumulated Net Unrealized Investment Gain (Loss)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
AOCI ending balance		82
AOCI, pre-tax		107
ASU 2017-12 \| Accumulated Net Unrealized Investment Gain (Loss) \| Available-for-sale securities
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
AOCI ending balance		(325)
ASU 2017-12 \| Accumulated Net Unrealized Investment Gain (Loss) \| Securities Held to Maturity
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
AOCI ending balance		407
Net investment hedges
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Gains (losses) recorded in AOCI	$ 34	$ 60

Accumulated Other Comprehensive Income (loss), before tax

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Accumulated change in equity from transactions and other events and circumstances from non-owner sources, net of tax effect, at period end. Excludes Net Income (Loss), and accumulated changes in equity from transactions resulting from investments by owners and distributions to owners. Includes foreign currency translation items, certain pension adjustments, unrealized gains and losses on certain investments in debt and equity securities, other than temporary impairment (OTTI) losses related to factors other than credit losses on available-for-sale and held-to-maturity debt securities that an entity does not intend to sell and it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis, as well as changes in the fair value of derivatives related to the effective portion of a designated cash flow hedge.

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Amount of investment in debt security measured at amortized cost (held-to-maturity).

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Amount after tax, before reclassification adjustments of other comprehensive income (loss).

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Amount after tax of other comprehensive income (loss) attributable to parent entity.

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