Mergers, Acquisitions, and Dispositions ProForma Impact of Merger (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended		9 Months Ended		12 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Business Acquisition, Pro Forma Revenue		$ 9,002	$ 8,545	$ 24,468	$ 26,129	$ 33,823
Business Acquisition, Pro Forma Net Income (Loss)		$ 501	$ 746	$ 1,346	$ 2,169	$ 2,618
Business Acquisition, Pro Forma Earnings Per Share, Basic		$ 0.5416	$ 0.8118	$ 1.4567	$ 2.3602	$ 2.8487
Business Acquisition, Pro Forma Earnings Per Share, Diluted		$ 0.5405	$ 0.8074	$ 1.4536	$ 2.3499	$ 2.8364
Noncash Merger Related Costs	[1],[2]			$ 508
Consolidation, Eliminations [Member]
Business Acquisition, Pro Forma Revenue	[3]		$ 192	171	$ 426	$ 559
Noncash Merger Related Costs	[3]	$ 20	$ 25	$ 660	$ 100	$ 92

[1] (e)Excludes $5 million of forgiveness of Accounts receivable related to merger commitments recorded in connection with the PHI Merger, the balance is included within Provision for uncollectible accounts.

[2] See Note 4 — Mergers, Acquisitions and Dispositions for additional information related to the merger with PHI.

[3] (a)The amounts above include adjustments for non-recurring costs directly related to the merger of $20 million and $660 million for the three and nine months ended September 30, 2016, respectively, and intercompany revenue of $171 million for the nine months ended September 30, 2016.