Income Taxes Level 4 (Details) - Summary of the Valuation Allowance - USD ($) $ in Millions	6 Months Ended		12 Months Ended
	Dec. 31, 2019	Jun. 30, 2019	Dec. 31, 2020	Dec. 31, 2018
Valuation Allowance [Line Items]
Disallowed interest expense carryforward				$ 283
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	$ 98	$ 525	$ 122	498
Changes in Related Gross Deferred Tax Assets/Liabilities	0	0	41	0
Charge / (Release)	24	$ (427)	54	27
Balance at End of Period	$ 122		$ 217	$ 525