Variable Interest Entities - Narrative (Details) - USD ($)	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Variable Interest Entity [Line Items]
Investments in LIHTC operating partnerships	$ 282,000,000	$ 248,000,000
Total Liabilities	1,000,000	2,000,000
Assets that can only be used to settle entities' obligations		0
Variable interest entity, liabilities		0
LIHTC Investments [Member]
Variable Interest Entity [Line Items]
Investments in LIHTC operating partnerships	6,405,000,000	5,932,000,000
Total Liabilities	2,526,000,000	2,569,000,000
LIHTC Investments [Member] \| Qualified affordable housing projects investment [Member]
Variable Interest Entity [Line Items]
Total Liabilities	546,000,000	532,000,000
Accrued Income And Other Assets [Member] \| LIHTC Investments [Member]
Variable Interest Entity [Line Items]
Investments in LIHTC operating partnerships	1,500,000,000	1,400,000,000
Investments [Member] \| LIHTC Investments [Member]
Variable Interest Entity [Line Items]
Amortization of investment	187,000,000	170,000,000
Tax credit of investment	184,000,000	166,000,000
Investments [Member] \| Guaranteed Funds [Member]
Variable Interest Entity [Line Items]
Assets that can only be used to settle entities' obligations	0
Variable interest entity, liabilities	0
Fair Value, Recurring [Member]
Variable Interest Entity [Line Items]
Other investments	$ 90,000,000	$ 115,000,000

The aggregate amount of recurring noncash expense charged against earnings in the period to allocate the cost of assets over their estimated remaining economic lives.

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Fair value of investment other than investment in equity security, investment in debt security and equity method investment. Includes, but is not limited to, investment in certain entities that calculate net asset value per share. Example includes, but is not limited to, investment in hedge fund, venture capital fund, private equity fund, and real estate partnership or fund.

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The amount deducted from an entities' taxes, reflecting a percentage of an amount invested in certain assets spread over the useful life of those assets; includes deferred investment tax credits.

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The carrying amount of the consolidated Variable Interest Entity's assets included in the reporting entity's statement of financial position.

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The carrying amount of the consolidated Variable Interest Entity's liabilities included in the reporting entity's statement of financial position.

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Carrying amount of the assets in the reporting entity's statement of financial position that relate to the reporting entity's variable interest in the Variable Interest Entity (VIE), where the reporting entity is not the VIE's primary beneficiary.

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Carrying amount of the liabilities in the reporting entity's statement of financial position that relate to the reporting entity's variable interest in the Variable Interest Entity (VIE), where the reporting entity is not the VIE's primary beneficiary.

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