Leases Leases (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Assets and Liabilities, Lessee [Abstract]
ROU asset	$ 1,314	$ 1,488
Cash paid for amounts included in the measurement of lease liability - operating cash flows	289	285
ROU assets obtained in exchange for new lease liabilities	$ 70	$ 341	$ 0
Weighted-average remaining lease term	8 years	8 years
Weighted-average discount rate	3.40%	3.30%
Lessee, Operating Lease, Liability, Payment, Due [Abstract]
2021	$ 283
2022	238
2023	219
2024	197
2025	185
Thereafter	553
Total undiscounted cash flows	1,675
Less: interest	205
Other Liabilities [Member]
Assets and Liabilities, Lessee [Abstract]
Lease liability	1,470	$ 1,654
Lessee, Operating Lease, Liability, Payment, Due [Abstract]
Lease liability	1,470	1,654
Lessee, Lease, Description [Line Items]
Lease liability	$ 1,470	$ 1,654

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Amount of lessee's undiscounted obligation for lease payment for operating lease.

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-Publisher FASB
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Amount of lessee's undiscounted obligation for lease payment for operating lease due after fifth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Amount of lessee's undiscounted obligation for lease payment for operating lease to be paid in next fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Amount of lessee's undiscounted obligation for lease payment for operating lease to be paid in fourth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Amount of lessee's undiscounted obligation for lease payment for operating lease to be paid in third fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Amount of lessee's undiscounted obligation for lease payment for operating lease to be paid in second fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Amount of lessee's undiscounted obligation for lease payments in excess of discounted obligation for lease payments for operating lease.

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Present value of lessee's discounted obligation for lease payments from operating lease.

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Amount of cash outflow from operating lease, excluding payments to bring another asset to condition and location necessary for its intended use.

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Amount of lessee's right to use underlying asset under operating lease.

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Weighted average discount rate for operating lease calculated at point in time.

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Weighted average remaining lease term for operating lease, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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Amount of increase in right-of-use asset obtained in exchange for operating lease liability.

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