Exit Activities and Discontinued Operations - Assets and Liabilities of Discontinued Operation (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Current
Total current assets	$ 448	$ 429
Non‑current
Total non‑current assets	2,584	2,680
Current
Total current liabilities	990	953
Non‑current
Total non‑current liabilities	1,717	1,894
Discontinued Operations, Held-for-sale
Current
Cash and cash equivalents	121	136
Discontinued Operations, Held-for-sale | EnerBank
Current
Cash and cash equivalents	121	136
Accounts receivable and other current assets	73	18
Notes receivable, allowance, current	28	32
Notes receivable, less allowance of $28 in 2021 and $32 in 2020	254	275
Total current assets	448	429
Non‑current
Plant, property, and equipment, net	27	22
Notes receivable, allowance, noncurrent	92	91
Notes receivable, less allowance of $92 in 2021 and $91 in 2020	2,511	2,612
Other non‑current assets	46	46
Total non‑current assets	2,584	2,680
Total assets	3,032	3,109
Current
Current portion of long-term debt	952	915
Accounts payable and other current liabilities	38	38
Total current liabilities	990	953
Non‑current
Long-term debt	1,715	1,890
Other non‑current liabilities	2	4
Total non‑current liabilities	1,717	1,894
Total liabilities	$ 2,707	$ 2,847