Taxation (Narrative) (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Jan. 30, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Examination [Line Items]
Unrecognized Tax Benefits		$ 76	$ 47	$ 14
Income Tax Credits and Adjustments		31	19
Valuation allowance		83	114
Unrecognized tax benefits that would affect the effective tax rate		45	28
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense		8	5
Liabilities recorded for tax-related interest and penalties		16	$ 8
Subsequent Event [Member]
Income Tax Examination [Line Items]
Tax Adjustments, Settlements, and Unusual Provisions	$ 23
Domestic Tax Authority [Member]
Income Tax Examination [Line Items]
Net operating loss carry-forwards		$ 407
Switzerland
Income Tax Examination [Line Items]
Applicable income tax rates		21.20%	7.83%	7.83%
Foreign Tax Authority [Member]
Income Tax Examination [Line Items]
Foreign tax credit carry-forward		$ 222
Bermuda
Income Tax Examination [Line Items]
Applicable income tax rates		0.00%
UNITED STATES
Income Tax Examination [Line Items]
Applicable income tax rates		21.00%
UNITED KINGDOM
Income Tax Examination [Line Items]
Applicable income tax rates		19.00%