Revisions of Previously Issued Financial Statements (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Increase (Decrease) in Other Operating Assets and Liabilities, Net	$ (61)	$ (12)
Net Cash Provided by (Used in) Operating Activities, Continuing Operations	495	226
Increase (Decrease) in Client Funds Held	6	2
Net Cash Provided by (Used in) Investing Activities	(215)	(290)
Net Cash Provided by (Used in) Financing Activities	827	29
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect	1,095	(69)
Cash, cash equivalents and restricted cash at beginning of period	563	532
Cash, Cash Equivalents, Restricted Cash at end of period	$ 1,658	463	$ 563
Previously Reported
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Increase (Decrease) in Other Operating Assets and Liabilities, Net			2
Net Cash Provided by (Used in) Operating Activities, Continuing Operations			628
Increase (Decrease) in Client Funds Held		(2)	(15)
Net Cash Provided by (Used in) Investing Activities		(292)	(527)
Net change in funds held for clients - financing		2	15
Net Cash Provided by (Used in) Financing Activities		33	(31)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect		(67)	40
Cash, cash equivalents and restricted cash at beginning of period		476	476
Cash, Cash Equivalents, Restricted Cash at end of period		409	516
Revision of Prior Period, Error Correction, Adjustment
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Increase (Decrease) in Other Operating Assets and Liabilities, Net			6
Net Cash Provided by (Used in) Operating Activities, Continuing Operations			6
Increase (Decrease) in Client Funds Held		2	15
Net Cash Provided by (Used in) Investing Activities		2	15
Net change in funds held for clients - financing		(4)	(30)
Net Cash Provided by (Used in) Financing Activities		(4)	(30)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect		(2)	(9)
Cash, cash equivalents and restricted cash at beginning of period		56	56
Cash, Cash Equivalents, Restricted Cash at end of period		54	47
As Revised
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Increase (Decrease) in Other Operating Assets and Liabilities, Net			8
Net Cash Provided by (Used in) Operating Activities, Continuing Operations			634
Increase (Decrease) in Client Funds Held		0	0
Net Cash Provided by (Used in) Investing Activities		(290)	(512)
Net change in funds held for clients - financing		(2)	(15)
Net Cash Provided by (Used in) Financing Activities		29	(61)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect		(69)	31
Cash, cash equivalents and restricted cash at beginning of period		532	532
Cash, Cash Equivalents, Restricted Cash at end of period		$ 463	$ 563

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Net change in funds held for clients - financing

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The increase (decrease) during the reporting period in the carrying amount of client funds held and maintained in custodial and separate accounts, and which are owned by clients or contract holders.

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Amount of increase (decrease) in operating assets after deduction of operating liabilities classified as other.

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Amount of cash inflow (outflow) from financing activities, including discontinued operations. Financing activity cash flows include obtaining resources from owners and providing them with a return on, and a return of, their investment; borrowing money and repaying amounts borrowed, or settling the obligation; and obtaining and paying for other resources obtained from creditors on long-term credit.

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Amount of cash inflow (outflow) from investing activities, including discontinued operations. Investing activity cash flows include making and collecting loans and acquiring and disposing of debt or equity instruments and property, plant, and equipment and other productive assets.

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Amount of cash inflow (outflow) from operating activities, excluding discontinued operations. Operating activity cash flows include transactions, adjustments, and changes in value not defined as investing or financing activities.

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