Leases (Narrative) (Detail) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2019
Lessor | New Corporate Office | Agreement with Lessor to Construct and Lease Corporate Office Property
Leases Disclosure [Line Items]
Amount of financing commitments to fund estimated project costs						$ 465
Leasing arrangement, charge		$ 71
Leasing arrangement, charge after tax		$ 53
Lease effective termination date		2021-04
Power Purchase Arrangement
Leases Disclosure [Line Items]
Rental revenue	$ 55		$ 53	$ 89	$ 85
Depreciation expense	$ 31		$ 27	$ 58	$ 50