Indexed Debt Securities (ZENS) and Securities Related to ZENS (CenterPoint Energy) (Details) $ / shares in Units, $ in Millions			6 Months Ended
		Jul. 17, 2018 USD ($)	Jun. 30, 2018 USD ($) shares $ / shares	Jun. 30, 2017 USD ($)	Jun. 14, 2018 $ / shares shares	Jan. 31, 2018 $ / shares	Dec. 31, 2017 USD ($) shares	Nov. 26, 2017 $ / shares
Cash paid per share exchanged | $ / shares			$ 72.00
Distribution To ZENS holders			$ 16	$ 0
Due to ZENS note holders			382				$ 0
Subordinated Debt ZENS [Member]
Principal amount of debt issued			1,000
Outstanding debt balance			$ 828
Subordinated note cash exchangeable percentage of fair value			95.00%
Contingent principal amount outstanding			$ 484
AT&T Common [Member]
Balance of investment owned (in shares) | shares			10,212,945
AT&T Common [Member] | Subordinated Debt ZENS [Member]
Number of shares referenced in exchangeable subordinated note | shares			0.7185
Charter Common [Member]
Balance of investment owned (in shares) | shares			872,503				872,503
Charter Common [Member] | Subordinated Debt ZENS [Member]
Number of shares referenced in exchangeable subordinated note | shares			0.061382				0.061382
Time Common [Member]
Balance of investment owned (in shares) | shares							888,392
ZENS early exchange ratio						100.00%
Time Common [Member] | Subordinated Debt ZENS [Member]
Number of shares referenced in exchangeable subordinated note | shares							0.0625
TW Common [Member]
Balance of investment owned (in shares) | shares							7,107,130
TW Common [Member] | Subordinated Debt ZENS [Member]
Number of shares referenced in exchangeable subordinated note | shares							0.5
AT&T To Acquire Time Warner [Member]
Due to ZENS note holders	[1]		$ 382
Indexed debt – reduction			(95)
Indexed debt securities derivative – reduction			(45)
Loss on indexed debt securities			242
AT&T To Acquire Time Warner [Member] | AT&T Common [Member]
Cash paid per share exchanged | $ / shares					$ 53.75
Fractional shares exchanged for each TW Common share held | shares					1.437
Cash proceeds received for shares exchanged			382
Total AT&T shares received in exchange for TW Common shares held | shares					10,212,945
Meredith to acquire Time [Member]
Distribution To ZENS holders			16
Indexed debt – reduction			(4)
Indexed debt securities derivative – reduction			(1)
Loss on indexed debt securities			11
Meredith to acquire Time [Member] | Time Common [Member]
Cash paid per share exchanged | $ / shares						$ 18.50		$ 18.50
Cash proceeds received for shares exchanged			$ 16
Subsequent Event [Member]
Distribution To ZENS holders		$ 382

[1] Cash of approximately $382 million was paid to ZENS note holders in July 2018.