Property and Equipment (Tables)

12 Months Ended

Dec. 31, 2020

The components of property and equipment were as follows:


(in millions)	Useful Lives	December 31, 2020		December 31, 2019

Land		$	236	$	—
Buildings and equipment	Up to 30 years	4,006		2,587
Wireless communications systems	Up to 20 years	49,453		34,353
Leasehold improvements	Up to 12 years	1,879		1,345
Capitalized software	Up to 10 years	16,412		12,705
Leased wireless devices	Up to 19 months	6,989		1,139
Construction in progress		4,595		2,973
Accumulated depreciation and amortization		(42,395)		(33,118)

Property and equipment, net		$	41,175	$	21,984

Activity in our asset retirement obligations was as follows:


(in millions)	Year Ended December 31, 2020		Year Ended December 31, 2019

Asset retirement obligations, beginning of year	$	659	$	609
Fair value of liabilities acquired through Merger	1,110		—
Liabilities incurred	16		35
Liabilities settled	(40)		(2)
Accretion expense	55		32
Changes in estimated cash flows	17		(15)

Asset retirement obligations, end of period	$	1,817	$	659

Classified on the balance sheet as:

Other current liabilities	$	14	$	—
Other long-term liabilities	1,803		659