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Stockholders' Equity - Change in AOCI Gain (Loss) by Component (Net of Tax) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2019	Mar. 31, 2018	Jan. 01, 2018
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
AOCI beginning balance	$ (1,263)	$ (926)	$ (949)
Cumulative effects from adoption of new accounting standards				$ (11)		$ 0
Effects from transfer of securities held to maturity to available for sale	888
Other comprehensive income (loss) before reclassifications	1,171	(302)	81
Amounts reclassified from AOCI into earnings	360	84	(58)
Other comprehensive income (loss), net of tax	1,531	(136)	23
AOCI ending balance	1,156	(1,263)	(926)
One time transfer of held to maturity securities	0	36,771
AOCI, pre-tax	1,200
Accumulated Net Unrealized Investment Gain (Loss) | Securities Available for Sale
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
AOCI beginning balance	(439)	17	(4)
Cumulative effects from adoption of new accounting standards						3
Effects from transfer of securities held to maturity to available for sale	724
Other comprehensive income (loss) before reclassifications	670	(293)	62
Amounts reclassified from AOCI into earnings	(20)	159	(41)
Other comprehensive income (loss), net of tax	650	(459)	21
AOCI ending balance	935	(439)	17
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)	(621)
Cumulative effects from adoption of new accounting standards						(113)
Effects from transfer of securities held to maturity to available for sale	164
Other comprehensive income (loss) before reclassifications	0	0	0
Amounts reclassified from AOCI into earnings	26	40	97
Other comprehensive income (loss), net of tax	26	447	97
AOCI ending balance	0	(190)	(524)
Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
AOCI beginning balance	(418)	(281)	(78)
Cumulative effects from adoption of new accounting standards						(63)
Effects from transfer of securities held to maturity to available for sale	0
Other comprehensive income (loss) before reclassifications	414	38	(95)
Amounts reclassified from AOCI into earnings	358	(112)	(108)
Other comprehensive income (loss), net of tax	772	(74)	(203)
AOCI ending balance	354	(418)	(281)
Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
AOCI beginning balance	(177)	(138)	(222)
Cumulative effects from adoption of new accounting standards						0
Effects from transfer of securities held to maturity to available for sale	0
Other comprehensive income (loss) before reclassifications	70	(39)	84
Amounts reclassified from AOCI into earnings	0	0	0
Other comprehensive income (loss), net of tax	70	(39)	84
AOCI ending balance	(107)	(177)	(138)
Other
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
AOCI beginning balance	(39)	0	(24)
Cumulative effects from adoption of new accounting standards						(28)
Effects from transfer of securities held to maturity to available for sale	0
Other comprehensive income (loss) before reclassifications	17	(8)	30
Amounts reclassified from AOCI into earnings	(4)	(3)	(6)
Other comprehensive income (loss), net of tax	13	(11)	24
AOCI ending balance	(26)	(39)	0
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Cumulative effects from adoption of new accounting standards						$ (201)
Effects from transfer of securities held to maturity to available for sale	888
ASU 2017-12
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Effects from transfer of securities held to maturity to available for sale					$ 82
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]
Effects from transfer of securities held to maturity to available for sale					82
AOCI, pre-tax					107
ASU 2017-12 | Accumulated Net Unrealized Investment Gain (Loss) | Securities Available for Sale
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Effects from transfer of securities held to maturity to available for sale					(325)
ASU 2017-12 | Accumulated Net Unrealized Investment Gain (Loss) | Securities Held to Maturity
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Effects from transfer of securities held to maturity to available for sale					407
ASU 2017-12 | Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Effects from transfer of securities held to maturity to available for sale					0
ASU 2017-12 | Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Effects from transfer of securities held to maturity to available for sale					0
ASU 2017-12 | Other
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Effects from transfer of securities held to maturity to available for sale					$ 0
Net investment hedges
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Gains (losses) recorded in AOCI	$ (49)	$ 150	$ (143)

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OCI. transfer of securities held to maturity to available for sale, 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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